Hook up ui::Compositor to Display's BeginFrameSource

cc/test/pixel_test_output_surface.cc

Index: cc/test/pixel_test_output_surface.cc
diff --git a/cc/test/pixel_test_output_surface.cc b/cc/test/pixel_test_output_surface.cc
index 883f809a8bdb3ea3a5092cb87f980264271534c9..9250ee44cc1bb9b5c026fd13c80d79a1ba8bcee5 100644
--- a/cc/test/pixel_test_output_surface.cc
+++ b/cc/test/pixel_test_output_surface.cc
@@ -5,6 +5,7 @@
 #include "cc/test/pixel_test_output_surface.h"
 
 #include "cc/output/output_surface_client.h"
+#include "cc/scheduler/begin_frame_source.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
@@ -12,8 +13,10 @@ namespace cc {
 PixelTestOutputSurface::PixelTestOutputSurface(
     scoped_refptr<ContextProvider> context_provider,
     scoped_refptr<ContextProvider> worker_context_provider,
-    bool flipped_output_surface)
+    bool flipped_output_surface,
+    std::unique_ptr<BeginFrameSource> begin_frame_source)
     : OutputSurface(context_provider, worker_context_provider),
+      begin_frame_source_(std::move(begin_frame_source)),
       external_stencil_test_(false) {
   capabilities_.adjust_deadline_for_parent = false;
   capabilities_.flipped_output_surface = flipped_output_surface;
@@ -21,17 +24,33 @@ PixelTestOutputSurface::PixelTestOutputSurface(
 
 PixelTestOutputSurface::PixelTestOutputSurface(
     scoped_refptr<ContextProvider> context_provider,
-    bool flipped_output_surface)
+    bool flipped_output_surface,
+    std::unique_ptr<BeginFrameSource> begin_frame_source)
     : PixelTestOutputSurface(context_provider,
                              nullptr,
-                             flipped_output_surface) {
-}
+                             flipped_output_surface,
+                             std::move(begin_frame_source)) {}
 
 PixelTestOutputSurface::PixelTestOutputSurface(
-    std::unique_ptr<SoftwareOutputDevice> software_device)
+    std::unique_ptr<SoftwareOutputDevice> software_device,
+    std::unique_ptr<BeginFrameSource> begin_frame_source)
     : OutputSurface(std::move(software_device)),
+      begin_frame_source_(std::move(begin_frame_source)),
       external_stencil_test_(false) {}
 
+PixelTestOutputSurface::~PixelTestOutputSurface() {}
+
+bool PixelTestOutputSurface::BindToClient(OutputSurfaceClient* client) {
+  if (!OutputSurface::BindToClient(client))
+    return false;
+
+  // TODO(enne): Once the renderer uses begin frame sources, this will
+  // always be valid.
+  if (begin_frame_source_)
+    client->SetBeginFrameSource(begin_frame_source_.get());
+  return true;
+}
+
 void PixelTestOutputSurface::Reshape(const gfx::Size& size,
                                      float scale_factor,
                                      bool has_alpha) {