Add observers to FrameSinkManagerHost.

content/browser/compositor/frame_sink_manager_host.h

Index: content/browser/compositor/frame_sink_manager_host.h
diff --git a/content/browser/compositor/frame_sink_manager_host.h b/content/browser/compositor/frame_sink_manager_host.h
index a4397302827a022c14adfc35c66369efafc538dd..4be010ff4ad2db92d32b1dffe5366d8eaa4055c0 100644
--- a/content/browser/compositor/frame_sink_manager_host.h
+++ b/content/browser/compositor/frame_sink_manager_host.h
@@ -5,10 +5,14 @@
 #ifndef CONTENT_BROWSER_COMPOSITOR_FRAME_SINK_MANAGER_HOST_H_
 #define CONTENT_BROWSER_COMPOSITOR_FRAME_SINK_MANAGER_HOST_H_
 
+#include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "cc/ipc/frame_sink_manager.mojom.h"
 #include "cc/surfaces/frame_sink_id.h"
+#include "cc/surfaces/surface_observer.h"
 #include "components/viz/frame_sinks/mojo_frame_sink_manager.h"
+#include "content/common/content_export.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
 namespace cc {
@@ -19,14 +23,18 @@ class SurfaceManager;
 namespace content {
 
 // Browser side implementation of mojom::FrameSinkManager. Manages frame sinks
-// and is inteded to replace SurfaceManager.
-class FrameSinkManagerHost : cc::mojom::FrameSinkManagerClient {
+// and is intended to replace SurfaceManager.
+class CONTENT_EXPORT FrameSinkManagerHost
+    : NON_EXPORTED_BASE(cc::mojom::FrameSinkManagerClient) {
  public:
   FrameSinkManagerHost();
   ~FrameSinkManagerHost() override;
 
   cc::SurfaceManager* surface_manager();
 
+  void AddObserver(cc::SurfaceObserver* observer);

[Fady Samuel, 2017/04/11 16:43:53]

Maybe I'm being pedantic but SurfaceObserver seems like a part of SurfaceManager
which is an implementation detail of the display compositor. I feel like we
should have a content-side observer.

[kylechar, 2017/04/11 16:52:39]

Ya, I think that's sounds totally reasonable to have a different observer base
type and maybe even different semantics.

Although, for now it might be easier to reuse SurfaceObserver because we can
then use it with both SurfaceManager or FrameSinkManagerHost. This will allow
using non-Mojo or Mojo at runtime based on a flag while performance is evaluated
(eg. for RendererCompositorFrameSink).

[kylechar, 2017/04/11 16:53:30]

If so, I should add a TODO saying as much.

[Fady Samuel, 2017/04/11 17:02:47]

It seems like those things are orthogonal.

FrameSinkManagerHost can observe SurfaceManager directly and forward
OnSurfaceCreated via another observer interface?

+  void RemoveObserver(cc::SurfaceObserver* observer);
+
   // See frame_sink_manager.mojom for descriptions.
   void CreateCompositorFrameSink(
       const cc::FrameSinkId& frame_sink_id,
@@ -53,6 +61,8 @@ class FrameSinkManagerHost : cc::mojom::FrameSinkManagerClient {
   // happen using Mojo. See http://crbug.com/657959.
   viz::MojoFrameSinkManager frame_sink_manager_;
 
+  base::ObserverList<cc::SurfaceObserver> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(FrameSinkManagerHost);
 };