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..e78a93df84c9a5ae1d508d595154073d08c8efb0 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(base::Callback<void(bool, double)> callback) override;
 
   void UpdateBrowserControlsState(blink::WebBrowserControlsState constraints,
                                   blink::WebBrowserControlsState current,
@@ -219,6 +222,25 @@ class CONTENT_EXPORT RenderWidgetCompositor
   cc::LayerTreeHost* layer_tree_host() { return layer_tree_host_.get(); }
 
  private:
+  class ReportTimeSwapPromise : public cc::SwapPromise {
+   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_;

[sunnyps, 2017/05/02 01:20:46]

nit: DISALLOW_COPY_AND_ASSIGN(ReportTimeSwapPromise) and also for
RenderWidgetCompositor since that's missing too

[panicker, 2017/05/02 21:21:36]

Done.

+  };
+
   void SetCompositorFrameSink(
       std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink);
   void LayoutAndUpdateLayers();