Bug 1107636 - Replace top-level RelativeLayout with <merge>. r=sebastian

Using systrace, I took 2 traces before and after. Using the slowest
of both traces, the first three measure passes had the following
improvements in CPU time:
  1) 20.583ms -> 13.149ms
  2) 1.695ms -> 0.827ms (1/2)
  3) 22.146ms -> 11.602ms (1/2)

This is to be expected – RelativeLayout requires two measure passes
so it makes sense to approximately half the measure times.

--HG--
extra : commitid : IDQckTgGsge
extra : rebase_source : df061c7645aa6b3a880278f75d3fa637e3160f9c

mobile/android/base/GeckoApp.java

@@ -170,7 +170,7 @@ public abstract class GeckoApp
     // after a version upgrade.
     private static final int CLEANUP_DEFERRAL_SECONDS = 15;
 
-    protected RelativeLayout mRootLayout;
+    protected View mRootLayout;
     protected RelativeLayout mMainLayout;
 
     protected RelativeLayout mGeckoLayout;
@@ -1385,7 +1385,7 @@ public abstract class GeckoApp
         setContentView(getLayout());
 
         // Set up Gecko layout.
-        mRootLayout = (RelativeLayout) findViewById(R.id.root_layout);
+        mRootLayout = findViewById(android.R.id.content);
         mGeckoLayout = (RelativeLayout) findViewById(R.id.gecko_layout);
         mMainLayout = (RelativeLayout) findViewById(R.id.main_layout);
         mLayerView = (LayerView) findViewById(R.id.layer_view);

mobile/android/base/resources/layout/gecko_app.xml

@@ -3,10 +3,7 @@
    - License, v. 2.0. If a copy of the MPL was not distributed with this
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 
-<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
-                android:id="@+id/root_layout"
-                android:layout_width="match_parent"
-                android:layout_height="match_parent">
+<merge xmlns:android="http://schemas.android.com/apk/res/android">
 
     <ViewStub android:id="@+id/tabs_panel"
               android:layout="@layout/tabs_panel_view"
@@ -150,4 +147,4 @@
               android:layout="@layout/button_toast"
               style="@style/Toast"/>
 
-</RelativeLayout>
+</merge>

mobile/android/base/resources/values/styles.xml

@@ -638,8 +638,6 @@
         <item name="android:background">@drawable/toast_background</item>
         <item name="android:layout_width">match_parent</item>
         <item name="android:layout_height">wrap_content</item>
-        <item name="android:layout_alignParentBottom">true</item>
-        <item name="android:layout_centerHorizontal">true</item>
         <item name="android:layout_gravity">bottom|center_horizontal</item>
         <item name="android:layout_marginBottom">64dp</item>
         <item name="android:layout_marginTop">0dp</item>