Don't drop all children when changing Android root layer.

content/browser/renderer_host/compositor_impl_android.h

Index: content/browser/renderer_host/compositor_impl_android.h
diff --git a/content/browser/renderer_host/compositor_impl_android.h b/content/browser/renderer_host/compositor_impl_android.h
index e3cc42e1ad56e9b43d6428bb2d67ed5e4bfd885a..4792d9058c7efd3c3b3ccf7109e6b7a7975ffe36 100644
--- a/content/browser/renderer_host/compositor_impl_android.h
+++ b/content/browser/renderer_host/compositor_impl_android.h
@@ -132,7 +132,11 @@ class CONTENT_EXPORT CompositorImpl
       bool is_transient);
   void OnGpuChannelEstablished();
 
+  // root_layer_ is the persistent internal root layer, while subroot_layer_
+  // is the one attached by the compositor client.
   scoped_refptr<cc::Layer> root_layer_;
+  scoped_refptr<cc::Layer> subroot_layer_;
+
   scoped_ptr<cc::LayerTreeHost> host_;
   content::UIResourceProviderImpl ui_resource_provider_;