How to display icon with back arrow in android toolbar like WhatsApp ?
I use below code to set back arrow & icon in toolbar.
 toolbar = (Toolbar) findViewById(R.id.toolbar);
 setSupportActionBar(toolbar);
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 getSupportActionBar().setDisplayShowHomeEnabled(true);
 getSupportActionBar().setHomeButtonEnabled(true);
 toolbar.setLogo(icon);
but i got result as below image.
 
 
I want icon immediate next after back arrow. I don't want any gap between back arrow & icon like below image of WhatsApp.

How to set icon with back arrow in toolbar like WhatsApp ?
You can achieve this result by creating a custom Drawable containing an arrow and image icon then add it to the toolbar toolbar.setNavigationIcon(drawable) as shown below.
        setSupportActionBar(mBinding.toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        Drawable drawable = new Drawable() {
            @Override
            public void draw(Canvas canvas) {
                int width = canvas.getWidth();
                int height = canvas.getHeight();
                Bitmap bMap = CircularImageView.getCircularBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.beautiful_eyes_small));    
                canvas.drawBitmap(bMap,(width-(bMap.getWidth())), (height/2)-(bMap.getHeight()/2), null);
                Bitmap bMap2 = BitmapFactory.decodeResource(getResources(), R.drawable.ic_arrow_back);
                canvas.drawBitmap(bMap2,0, (height/2)-(bMap2.getHeight()/2), null);
            }
            @Override
            public void setAlpha(int i) {
            }
            @Override
            public void setColorFilter(ColorFilter colorFilter) {
            }
            @Override
            public int getOpacity() {
                return PixelFormat.TRANSLUCENT;
            }
        };
        mBinding.toolbar.setNavigationIcon(drawable);

As far as I Know, WhatsApp is not using App-compat Support Library Toolbar, Whatsapp is setting the Custom Action Bar using
actionBar.setCustomView(R.layout.conversation_actionbar);
Attached is the conversation_actionbar.xml , Whatsapp is using
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@id/custom_view"
android:layout_width="fill_parent"
android:layout_height="?actionBarSize"
android:clipChildren="false" >
<LinearLayout
    android:id="@id/back"
    style="@style/ActionBarButtonStyle"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_centerVertical="true"
    android:contentDescription="@string/abc_action_bar_up_description"
    android:enabled="false"
    android:orientation="horizontal"
    android:padding="@dimen/abc_action_bar_default_padding_material" >
    <ImageView
        android:id="@id/up"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left|center"
        android:scaleType="center"
        android:src="?homeAsUpIndicator" />
    <FrameLayout
        android:id="@id/conversation_contact_photo_frame"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left|center"
        android:layout_marginRight="0.0dip" >
        <ImageView
            android:id="@id/conversation_contact_photo"
            android:layout_width="35.0dip"
            android:layout_height="35.0dip"
            android:scaleType="fitCenter" />
        <View
            android:id="@id/transition_start"
            android:layout_width="35.0dip"
            android:layout_height="35.0dip" />
        <ProgressBar
            android:id="@id/change_photo_progress"
            style="?android:attr/progressBarStyleSmallInverse"
            android:layout_width="35.0dip"
            android:layout_height="35.0dip"
            android:layout_gravity="center"
            android:visibility="gone" />
    </FrameLayout>
</LinearLayout>
<LinearLayout
    android:id="@id/conversation_contact"
    style="@style/ActionBarButtonStyle"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_centerVertical="true"
    android:layout_toRightOf="@id/back"
    android:clickable="true"
    android:clipChildren="false"
    android:orientation="vertical"
    android:paddingBottom="2.0dip"
    android:paddingLeft="4.0dip"
    android:paddingRight="0.0dip"
    android:paddingTop="0.0dip" >
    <com.whatsapp.TextEmojiLabel
        android:id="@id/conversation_contact_name"
        style="@style/Theme.ActionBar.TitleTextStyle.Condensed"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:ellipsize="end"
        android:gravity="left"
        android:lines="1"
        android:scrollHorizontally="true"
        android:singleLine="true" />
    <LinearLayout
        android:id="@id/conversation_contact_status_holder"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:clipChildren="false"
        android:clipToPadding="false"
        android:orientation="horizontal" >
        <TextView
            android:id="@id/conversation_contact_status_prefix"
            style="@style/Theme.ActionBar.SubtitleTextStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="left"
            android:lines="1"
            android:paddingRight="3.5sp"
            android:singleLine="true"
            android:text="@string/conversation_last_seen"
            android:visibility="gone" />
        <TextView
            android:id="@id/conversation_contact_status"
            style="@style/Theme.ActionBar.SubtitleTextStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="left"
            android:ellipsize="end"
            android:lines="1"
            android:singleLine="true" />
        <View
            android:layout_width="0.0dip"
            android:layout_height="1.0dip"
            android:layout_weight="1.0" />
    </LinearLayout>
</LinearLayout>
But I would suggest you to follow Materail Design Rules and use ToolBar of App-compat Support Library,
You can get the following result as shown in the Picture below
By using following code
your_activity.xml:
<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar_chats"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light">
            <include layout="@layout/toolbar_conversation"/>
</android.support.v7.widget.Toolbar>
</android.support.design.widget.AppBarLayout>
toolbar_conversation.xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:background="?attr/selectableItemBackgroundBorderless"
android:layout_width="fill_parent"
android:layout_height="?actionBarSize"
>
<!-- android:background="?attr/selectableItemBackgroundBorderless" will cause this Custom View to make ripple effect -->
<LinearLayout
    android:id="@+id/conversation_image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_centerVertical="true"
    android:contentDescription="@string/abc_action_bar_up_description"
    android:orientation="horizontal">
        <ImageView
            android:id="@+id/conversation_contact_photo"
            android:layout_width="35.0dip"
            android:layout_height="35.0dip"
            android:src="@drawable/icon"
            android:scaleType="fitCenter" />
</LinearLayout>
<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_centerVertical="true"
    android:layout_toRightOf="@id/conversation_image"
    android:orientation="vertical"
    android:paddingBottom="2.0dip"
    android:paddingLeft="4.0dip"
    android:paddingRight="0.0dip"
    android:paddingTop="0.0dip" >
    <TextView
        android:id="@+id/action_bar_title_1"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="6dp"
        android:layout_weight="0.6"
        android:ellipsize="end"
        android:gravity="center_vertical"
        android:maxLines="1"
        android:textSize="18sp"
        android:text="shanraisshan"
        android:textStyle="bold" />
    <TextView
        android:id="@+id/action_bar_title_2"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_marginLeft="6dp"
        android:layout_weight="0.4"
        android:ellipsize="end"
        android:text="last seen 1 hour ago"
        android:maxLines="1"
        android:textSize="12sp" />
</LinearLayout>
Activity.java
final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar_chats);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
toolbar.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Log.e("Toolbar","Clicked");
    }
});
Just wait for it, Whatsapp will shift to App-compat Support Library in future.
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