Refactoring the way begin frame sources inside scheduler work.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 7f6ae44ff74ef374156cae786bf66e6d54bdcd0a..dfddb1caaf9190f2bfc975cc973e7a67750fbcf1 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -213,7 +213,8 @@ LayerTreeHostImpl::LayerTreeHostImpl(
     RenderingStatsInstrumentation* rendering_stats_instrumentation,
     SharedBitmapManager* manager,
     int id)
-    : client_(client),
+    : BaseBeginFrameSource(0),
+      client_(client),
       proxy_(proxy),
       use_gpu_rasterization_(false),
       input_handler_client_(NULL),
@@ -1329,7 +1330,7 @@ void LayerTreeHostImpl::SetNeedsRedrawRect(const gfx::Rect& damage_rect) {
 }
 
 void LayerTreeHostImpl::BeginFrame(const BeginFrameArgs& args) {
-  client_->BeginFrame(args);
+  frame_sink_->BeginFrame(args);
 }
 
 void LayerTreeHostImpl::DidSwapBuffers() {
@@ -1564,11 +1565,15 @@ bool LayerTreeHostImpl::SwapBuffers(const LayerTreeHostImpl::FrameData& frame) {
   return true;
 }
 
-void LayerTreeHostImpl::SetNeedsBeginFrame(bool enable) {
+void LayerTreeHostImpl::OnGenerateChange(bool generate_frames) {
   if (output_surface_)
-    output_surface_->SetNeedsBeginFrame(enable);
+    output_surface_->SetNeedsBeginFrame(generate_frames);
   else
-    DCHECK(!enable);
+    DCHECK(!generate_frames);
+}
+
+std::string LayerTreeHostImpl::TypeString() const {
+  return "LayerTreeHostImpl";
 }
 
 void LayerTreeHostImpl::WillBeginImplFrame(const BeginFrameArgs& args) {