[Android] Fix highlight for toolbar buttons

This CL fixes the button highlight when toolbar buttons are focused
using a keyboard. There are two unrelated fixes:
1. ToggleTabStackButton now inherits ChromeImageButton instead of
   generic ImageButton.
2. ToolbarMenuButtonPhone style no longer forces the background to be
   null, keeping selectableItemBackground set by ToolbarButton style.

Bug: 955037
Change-Id: Idc20378c9660dc0d95189af5efc417dd861512da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1725909
Commit-Queue: Theresa <twellington@chromium.org>
Auto-Submit: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682259}

chrome/android/java/res/values-v17/styles.xml

@@ -701,7 +701,6 @@
     <style name="ToolbarMenuButtonPhone" parent="ToolbarButton">
         <item name="android:layout_gravity">top</item>
         <item name="android:paddingEnd">8dp</item>
-        <item name="android:background">@null</item>
     </style>
     <style name="ToolbarMenuButtonTablet" parent="ToolbarButton">
         <item name="android:layout_width">43dp</item>

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/ToggleTabStackButton.java

@@ -8,21 +8,21 @@ import android.content.Context;
 import android.support.annotation.Nullable;
 import android.util.AttributeSet;
 import android.view.View;
-import android.widget.ImageButton;
 
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.toolbar.TabCountProvider;
 import org.chromium.chrome.browser.toolbar.TabSwitcherDrawable;
 import org.chromium.chrome.browser.util.AccessibilityUtil;
+import org.chromium.ui.widget.ChromeImageButton;
 
 /**
  * A button displaying the number of open tabs. Clicking the button toggles the tab switcher view.
  * TODO(twellington): Replace with TabSwitcherButtonCoordinator so code can be shared with bottom
  *                    toolbar.
  */
-public class ToggleTabStackButton extends ImageButton implements TabCountProvider.TabCountObserver,
-                                                                 View.OnClickListener,
-                                                                 View.OnLongClickListener {
+public class ToggleTabStackButton
+        extends ChromeImageButton implements TabCountProvider.TabCountObserver,
+                                             View.OnClickListener, View.OnLongClickListener {
     private TabSwitcherDrawable mTabSwitcherButtonDrawable;
     private TabSwitcherDrawable mTabSwitcherButtonDrawableLight;
     private TabCountProvider mTabCountProvider;