Use swap-promise to improve first* paint times

content/renderer/gpu/render_widget_compositor.h

Index: content/renderer/gpu/render_widget_compositor.h
diff --git a/content/renderer/gpu/render_widget_compositor.h b/content/renderer/gpu/render_widget_compositor.h
index a36b5f02b7ca12b46ed11b93f202fe78fd97801f..a2692a09c1d847d2ce18a3f04daa7bd318f33a54 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -53,6 +53,8 @@ class CONTENT_EXPORT RenderWidgetCompositor
     : NON_EXPORTED_BASE(public blink::WebLayerTreeView),
       NON_EXPORTED_BASE(public cc::LayerTreeHostClient),
       NON_EXPORTED_BASE(public cc::LayerTreeHostSingleThreadClient) {
+  using ReportTimeCallback = base::Callback<void(bool, double)>;
+
  public:
   // Attempt to construct and initialize a compositor instance for the widget
   // with the given settings. Returns NULL if initialization fails.
@@ -167,6 +169,7 @@ class CONTENT_EXPORT RenderWidgetCompositor
   void SetShowPaintRects(bool show) override;
   void SetShowDebugBorders(bool show) override;
   void SetShowScrollBottleneckRects(bool show) override;
+  void NotifySwapTime(ReportTimeCallback callback) override;
 
   void UpdateBrowserControlsState(blink::WebBrowserControlsState constraints,
                                   blink::WebBrowserControlsState current,
@@ -240,6 +243,8 @@ class CONTENT_EXPORT RenderWidgetCompositor
   cc::FrameSinkId frame_sink_id_;
 
   base::WeakPtrFactory<RenderWidgetCompositor> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderWidgetCompositor);
 };
 
 }  // namespace content