🏠 Add expand button and flag to enable it

chrome/android/java/res/layout/bottom_control_container.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2016 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
 <org.chromium.chrome.browser.widget.bottomsheet.BottomSheet
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/bottom_sheet"
     android:layout_width="match_parent"
     android:layout_height="wrap_content" >
@@ skipping 15 matching lines @@
                 android:layout_width="match_parent"
                 android:layout_height="@dimen/toolbar_shadow_height"
                 android:src="@drawable/toolbar_shadow"
                 android:scaleType="fitXY"
                 android:scaleY="-1"
                 android:contentDescription="@null" />
 
             <FrameLayout
                 android:id="@+id/toolbar_holder"
                 android:layout_width="match_parent"
-                android:layout_height="@dimen/bottom_control_container_height"
+                android:layout_height="match_parent"
                 android:layout_marginTop="@dimen/toolbar_shadow_height" >
 
                 <ViewStub
                     android:id="@+id/toolbar_stub"
                     android:layout_width="match_parent"
                     android:layout_height="match_parent" />
 
             </FrameLayout>
 
             <ImageView
@@ skipping 31 matching lines @@
 
     <ImageView
         android:id="@+id/toolbar_shadow"
         android:src="@drawable/bottom_toolbar_shadow"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:scaleType="fitXY"
         android:contentDescription="@null" />
 
 </org.chromium.chrome.browser.widget.bottomsheet.BottomSheet>