Gray top border for keyboard accessory.

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

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2015 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. -->
 
 <merge xmlns:android="http://schemas.android.com/apk/res/android">
     <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:orientation="vertical">
 
-        <org.chromium.chrome.browser.compositor.CompositorViewHolder
-            android:id="@+id/compositor_view_holder"
-            android:layout_width="match_parent"
+        <RelativeLayout

[newt (away), 2015/08/06 03:27:22]

No more nesting :O

We've already introduced one new layer of nesting above the main View (which
slows down every input event, every layout, etc), let's avoid adding more if at
all possible.

Is it possible? Yes! If you simply give the keyboard_accessory a top margin of
-2dp, and then build the shadow into the keyboard_accessory view, that should
work nicely.

Also, there's a FadingShadowView, which may be handy here (It's specifically
designed for cases where the shadow needs to fade in a fade out, like on the
bottom of the new tab page, but it would work here too). It's currently in
chrome/ but can be moved to ui/. Using keyboard_accessory_shadow.xml is also
fine.

[please use gerrit instead, 2015/08/07 18:43:28]

I've placed the shadow inside of the keyboard accessory and made it overlap
content by 2dp, which is the size of the shadow. However, this produces
artifacts as seen in

https://drive.google.com/a/google.com/file/d/0BwnAxYoFTeYPdl93WlVxT0dYYm8

It's as if the content is not redrawing under the shadow. Did I miss something
obvious?

             android:layout_height="0dp"
-            android:layout_weight="1" />
+            android:layout_weight="1"
+            android:layout_width="match_parent">
+
+            <org.chromium.chrome.browser.compositor.CompositorViewHolder
+                android:id="@+id/compositor_view_holder"
+                android:layout_alignParentBottom="true"
+                android:layout_height="match_parent"
+                android:layout_width="match_parent" />
+
+            <View
+                android:id="@+id/keyboard_accessory_shadow"
+                android:layout_alignParentBottom="true"
+                android:layout_height="2dp"
+                android:layout_width="match_parent"
+                android:background="@drawable/keyboard_accessory_shadow"
+                android:visibility="gone" />
+        </RelativeLayout>
 
         <HorizontalScrollView
             android:id="@+id/keyboard_accessory"
             android:layout_height="@dimen/keyboard_accessory_height"
             android:layout_width="match_parent"
             android:background="#FFF"
             android:scrollbars="none"
             android:visibility="gone" />
     </LinearLayout>
 
@@ skipping 24 matching lines @@
         android:layout_height="match_parent"
         />
     <!-- This empty view is used as the anchor for custom menu -->
     <View
         android:id="@+id/menu_anchor_stub"
         android:layout_width="0px"
         android:layout_height="0px"
         android:layout_gravity="bottom|start"
         />
 </merge>