Cleanup Bookmarks, History, and SavedPages screen

- Redesigned bookmark thumbnail view
- Custom ImageView to scale the thumbnail properly
- Fix column count in bookmark expandable view
- Disable GroupView if we have only one account in bookmark

Change-Id: I2fccae50b9e96c909744bd5c7d0af7b373136c54
diff --git a/res/layout/snapshots.xml b/res/layout/snapshots.xml
index a02fbb9..045a418 100644
--- a/res/layout/snapshots.xml
+++ b/res/layout/snapshots.xml
@@ -18,7 +18,7 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:paddingTop="@dimen/combo_paddingTop">
+    android:paddingTop="@dimen/combo_snapshot_paddingTop">
 
     <com.android.browser.view.SnapshotGridView
         android:id="@+id/grid"
@@ -37,4 +37,10 @@
         android:text="@string/empty_snapshots_folder"
         android:visibility="gone" />
 
+    <View
+        android:layout_width="match_parent"
+        android:layout_height="@dimen/combo_shadow_height"
+        android:layout_gravity="top"
+        android:background="@drawable/shadow_bottom" />
+
 </FrameLayout>