Make ViewRoot the top of the ViewAndroid tree

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 6d49a396a9d8be47d62bc53da8db711ab1200ab8..8c8bc716f1f1946bc2cb5ba2e9437a05b9c14c53 100644
--- a/content/browser/renderer_host/compositor_impl_android.h
+++ b/content/browser/renderer_host/compositor_impl_android.h
@@ -40,6 +40,10 @@ class OutputSurface;
 class VulkanContextProvider;
 }
 
+namespace ui {
+class ViewRoot;
+}
+
 namespace content {
 class CompositorClient;
 
@@ -53,7 +57,7 @@ class CONTENT_EXPORT CompositorImpl
       public ui::UIResourceProvider,
       public ui::WindowAndroidCompositor {
  public:
-  CompositorImpl(CompositorClient* client, gfx::NativeWindow root_window);
+  CompositorImpl(CompositorClient* client, ui::ViewRoot* view_root);
   ~CompositorImpl() override;
 
   static bool IsInitialized();
@@ -127,8 +131,8 @@ class CONTENT_EXPORT CompositorImpl
 
   cc::FrameSinkId frame_sink_id_;
 
-  // root_layer_ is the persistent internal root layer, while subroot_layer_
-  // is the one attached by the compositor client.
+  // Layer in |view_root_| is the persistent internal root layer,
+  // while subroot_layer_ is the one attached by the compositor client.
   scoped_refptr<cc::Layer> subroot_layer_;
 
   // Subtree for hidden layers with CopyOutputRequests on them.
@@ -150,6 +154,7 @@ class CONTENT_EXPORT CompositorImpl
   CompositorClient* client_;
 
   gfx::NativeWindow root_window_;
+  ui::ViewRoot* view_root_;
 
   // Whether we need to update animations on the next composite.
   bool needs_animate_;