mus: Embedder can request and observe BeginFrame for embedded client.

ui/aura/mus/window_port_mus.cc

Index: ui/aura/mus/window_port_mus.cc
diff --git a/ui/aura/mus/window_port_mus.cc b/ui/aura/mus/window_port_mus.cc
index 4c98ed4558a036614237a01cf0d8aa1497009064..ee4d46d91d6934da11332f0aa60affbd3773a9b9 100644
--- a/ui/aura/mus/window_port_mus.cc
+++ b/ui/aura/mus/window_port_mus.cc
@@ -5,6 +5,7 @@
 #include "ui/aura/mus/window_port_mus.h"
 
 #include "base/memory/ptr_util.h"
+#include "cc/ipc/frame_sink_manager.mojom.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/transient_window_client.h"
 #include "ui/aura/mus/client_surface_embedder.h"
@@ -34,6 +35,27 @@ WindowPortMus::WindowMusChangeDataImpl::WindowMusChangeDataImpl() = default;
 
 WindowPortMus::WindowMusChangeDataImpl::~WindowMusChangeDataImpl() = default;
 
+class WindowPortMus::FrameSinkObserver : public cc::mojom::FrameSinkObserver {
+ public:
+  explicit FrameSinkObserver(base::RepeatingClosure begin_frame_callback)
+      : binding_(this),
+        begin_frame_callback_(std::move(begin_frame_callback)) {}
+  ~FrameSinkObserver() override {}
+
+  cc::mojom::FrameSinkObserverPtr GetPtr() {
+    return binding_.CreateInterfacePtrAndBind();
+  }
+
+ private:
+  // cc::mojom::FrameSinkObserver:
+  void OnBeginFrame() override { begin_frame_callback_.Run(); }
+
+  mojo::Binding<cc::mojom::FrameSinkObserver> binding_;
+  base::RepeatingClosure begin_frame_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(FrameSinkObserver);
+};
+
 // static
 WindowMus* WindowMus::Get(Window* window) {
   return WindowPortMus::Get(window);
@@ -531,6 +553,19 @@ cc::SurfaceId WindowPortMus::GetSurfaceId() const {
   return cc::SurfaceId();
 }
 
+void WindowPortMus::SetNeedsBeginFrames(bool needs,
+                                        base::RepeatingClosure callback) {
+  if (!needs) {
+    frame_sink_observer_ = nullptr;
+    return;
+  }
+  if (frame_sink_observer_)
+    return;
+  frame_sink_observer_ =
+      base::MakeUnique<FrameSinkObserver>(std::move(callback));
+  window_tree_client_->RequestBeginFrames(this, frame_sink_observer_->GetPtr());
+}
+
 void WindowPortMus::UpdatePrimarySurfaceInfo() {
   bool embeds_surface = window_mus_type() == WindowMusType::TOP_LEVEL_IN_WM ||
                         window_mus_type() == WindowMusType::EMBED_IN_OWNER;