Notification custom layouts: paint the button icon for Material.

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

Index: chrome/android/java/res/layout/web_notification_button.xml
diff --git a/chrome/android/java/res/layout/web_notification_button.xml b/chrome/android/java/res/layout/web_notification_button.xml
index 37cef2b9eb67556e0f2ef4240db9dcee96994ce2..dd03d6f7e35e1561970e50fdf83fcb6f728d24a7 100644
--- a/chrome/android/java/res/layout/web_notification_button.xml
+++ b/chrome/android/java/res/layout/web_notification_button.xml
@@ -3,15 +3,41 @@
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
-<Button xmlns:android="http://schemas.android.com/apk/res/android"
-    android:drawablePadding="0dp"
-    android:ellipsize="end"
-    android:gravity="start|center_vertical"
-    android:id="@+id/button"
-    android:layout_height="48dp"
-    android:layout_weight="1"
+<!--
+    Overlays a Button on top of an ImageView. Via a RemoteViews the only way to set an image, apply
+    a color filter, and have API level 16+ compatibility, is to use an ImageView. There are some
+    similar methods for Button but they are either hidden, require too high an API level, or both.
+
+    The Button must be on top of the ImageView so that it can be tapped, and so that its text will
+    be read out by TalkBack.
+-->
+<FrameLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    tools:ignore="MergeRootFrame"
     android:layout_width="0dp"
-    android:paddingStart="8dp"
-    android:singleLine="true"
-    android:textSize="13sp"
-    style="@style/WebNotificationButton"/>
+    android:layout_height="48dp"
+    android:layout_weight="1">
+
+    <ImageView
+        android:id="@+id/button_icon"
+        android:layout_width="wrap_content"
+        android:layout_height="match_parent"
+        android:layout_marginStart="8dp"
+        android:layout_gravity="start|center_vertical"
+        android:maxWidth="48dp"
+        android:contentDescription="@null"
+        android:scaleType="centerInside"/>
+
+    <Button
+        android:id="@+id/button"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:ellipsize="end"
+        android:gravity="start|center_vertical"
+        android:paddingStart="8dp"
+        android:singleLine="true"
+        android:textSize="13sp"
+        style="@style/WebNotificationButton"/>
+
+</FrameLayout>