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..3347026ab19dc33b029e14103de794053cadd32d 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,
@@ -219,6 +222,27 @@ class CONTENT_EXPORT RenderWidgetCompositor
   cc::LayerTreeHost* layer_tree_host() { return layer_tree_host_.get(); }
 
  private:
+  class ReportTimeSwapPromise : public cc::SwapPromise {

[sunnyps, 2017/05/05 00:12:14]

nit: Can you move this to the .cc file? It doesn't have to be an inner class and
can go in an anonymous namespace instead.

[panicker, 2017/05/05 00:21:14]

Done.

+   public:
+    ReportTimeSwapPromise(
+        ReportTimeCallback callback,
+        const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
+    ~ReportTimeSwapPromise() override;
+
+    void DidActivate() override {}
+    void WillSwap(cc::CompositorFrameMetadata* metadata) override {}
+    void DidSwap() override;
+    DidNotSwapAction DidNotSwap(DidNotSwapReason reason) override;
+
+    int64_t TraceId() const override;
+
+   private:
+    ReportTimeCallback callback_;
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+    DISALLOW_COPY_AND_ASSIGN(ReportTimeSwapPromise);
+  };
+
   void SetCompositorFrameSink(
       std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink);
   void LayoutAndUpdateLayers();
@@ -240,6 +264,8 @@ class CONTENT_EXPORT RenderWidgetCompositor
   cc::FrameSinkId frame_sink_id_;
 
   base::WeakPtrFactory<RenderWidgetCompositor> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderWidgetCompositor);
 };
 
 }  // namespace content