Use swap-promise to improve first* paint times

content/renderer/gpu/render_widget_compositor.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 #define CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 35 matching lines @@
 
 namespace content {
 
 class RenderWidgetCompositorDelegate;
 struct ScreenInfo;
 
 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.
   static std::unique_ptr<RenderWidgetCompositor> Create(
       RenderWidgetCompositorDelegate* delegate,
       CompositorDependencies* compositor_deps);
 
   ~RenderWidgetCompositor() override;
 
   static cc::LayerTreeSettings GenerateLayerTreeSettings(
@@ skipping 94 matching lines @@
   void UpdateEventRectsForSubframeIfNecessary() override;
   blink::WebEventListenerProperties EventListenerProperties(
       blink::WebEventListenerClass eventClass) const override;
   void SetHaveScrollEventHandlers(bool) override;
   bool HaveScrollEventHandlers() const override;
   int LayerTreeId() const override;
   void SetShowFPSCounter(bool show) override;
   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,
                                   bool animate) override;
   void SetBrowserControlsHeight(float height, bool shrink) override;
   void SetBrowserControlsShownRatio(float) override;
   // TODO(ianwen): Move this method to WebLayerTreeView and implement main
   // thread scrolling.
   virtual void setBottomControlsHeight(float height);
 
@@ skipping 32 matching lines @@
 
  protected:
   friend class RenderViewImplScaleFactorTest;
 
   RenderWidgetCompositor(RenderWidgetCompositorDelegate* delegate,
                          CompositorDependencies* compositor_deps);
 
   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();
   void InvokeLayoutAndPaintCallback();
   bool CompositeIsSynchronous() const;
   void SynchronouslyComposite();
 
   int num_failed_recreate_attempts_;
   RenderWidgetCompositorDelegate* const delegate_;
   CompositorDependencies* const compositor_deps_;
   const bool threaded_;
   std::unique_ptr<cc::AnimationHost> animation_host_;
   std::unique_ptr<cc::LayerTreeHost> layer_tree_host_;
   bool never_visible_;
   bool is_for_oopif_;
 
   blink::WebLayoutAndPaintAsyncCallback* layout_and_paint_async_callback_;
 
   cc::FrameSinkId frame_sink_id_;
 
   base::WeakPtrFactory<RenderWidgetCompositor> weak_factory_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_