Make ui::Snapshot asynchronous on Android, remove CompositeAndReadback.

ui/base/android/window_android_compositor.h

Index: ui/base/android/window_android_compositor.h
diff --git a/ui/base/android/window_android_compositor.h b/ui/base/android/window_android_compositor.h
index 1c2fefcdd64544e183b781ec56aadf60e610ca17..e1de9d4e2d421925451dd54983124f32b08f9504 100644
--- a/ui/base/android/window_android_compositor.h
+++ b/ui/base/android/window_android_compositor.h
@@ -8,6 +8,7 @@
 #include "ui/base/ui_base_export.h"
 
 namespace cc {
+class CopyOutputRequest;
 class Layer;
 }
 
@@ -19,6 +20,8 @@ class UI_BASE_EXPORT WindowAndroidCompositor {
   virtual ~WindowAndroidCompositor() {}
 
   virtual void AttachLayerForReadback(scoped_refptr<cc::Layer> layer) = 0;
+  virtual void RequestCopyOfOutputOnRootLayer(
+      scoped_ptr<cc::CopyOutputRequest> request) = 0;
   virtual void OnVSync(base::TimeTicks frame_time,
                        base::TimeDelta vsync_period) = 0;
 };