Cleaning up compositing field trial code and enable FCM in beta/stable

content/browser/renderer_host/render_widget_host_impl.h

Index: content/browser/renderer_host/render_widget_host_impl.h
diff --git a/content/browser/renderer_host/render_widget_host_impl.h b/content/browser/renderer_host/render_widget_host_impl.h
index b7a528e2104f2a476d8331b6cda2eaa63825b938..c4c9580ee0ca4f81439fe74c663b12d9bac01a51 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -629,6 +629,9 @@ class CONTENT_EXPORT RenderWidgetHostImpl : virtual public RenderWidgetHost,
   // True when a page is rendered directly via the GPU process.
   bool is_accelerated_compositing_active_;
 
+  // True if threaded compositing is enabled on this view.
+  bool is_threaded_compositing_enabled_;
+
   // Set if we are waiting for a repaint ack for the view.
   bool repaint_ack_pending_;