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

content/browser/renderer_host/compositor_impl_android.cc

 // Copyright (c) 2012 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.
 
 #include "content/browser/renderer_host/compositor_impl_android.h"
 
 #include <android/bitmap.h>
 #include <android/native_window_jni.h>
 
 #include "base/android/jni_android.h"
@@ skipping 323 matching lines @@
 
 void CompositorImpl::OnGpuChannelEstablished() {
   ScheduleComposite();
 }
 
 UIResourceProvider& CompositorImpl::GetUIResourceProvider() {
   return ui_resource_provider_;
 }
 
 void CompositorImpl::SetRootLayer(scoped_refptr<cc::Layer> root_layer) {
-  root_layer_->RemoveAllChildren();
-  if (root_layer)
+  if (subroot_layer_) {
+    subroot_layer_->RemoveFromParent();
+    subroot_layer_ = NULL;
+  }
+  if (root_layer) {
+    subroot_layer_ = root_layer;
     root_layer_->AddChild(root_layer);
+  }
 }
 
 void CompositorImpl::SetWindowSurface(ANativeWindow* window) {
   GpuSurfaceTracker* tracker = GpuSurfaceTracker::Get();
 
   if (window_) {
     tracker->RemoveSurface(surface_id_);
     ANativeWindow_release(window_);
     window_ = NULL;
     surface_id_ = 0;
@@ skipping 260 matching lines @@
 }
 
 void CompositorImpl::SetNeedsAnimate() {
   if (!host_)
     return;
 
   host_->SetNeedsAnimate();
 }
 
 }  // namespace content