Fix Omnibox.CharTypedToRepaintLatency regression with D3DVsync experiment

content/browser/compositor/gpu_vsync_begin_frame_source.h

 // Copyright 2016 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_BROWSER_COMPOSITOR_GPU_VSYNC_BEGIN_FRAME_SOURCE_H_
 #define CONTENT_BROWSER_COMPOSITOR_GPU_VSYNC_BEGIN_FRAME_SOURCE_H_
 
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "cc/scheduler/begin_frame_source.h"
+#include "content/common/content_export.h"
 
 namespace content {
 
 // This class is used to control VSync production on GPU side.
-class GpuVSyncControl {
+class CONTENT_EXPORT GpuVSyncControl {
  public:
   virtual void SetNeedsVSync(bool needs_vsync) = 0;
 };
 
 // This is a type of ExternalBeginFrameSource where VSync signals are
 // generated externally on GPU side.
-class GpuVSyncBeginFrameSource : public cc::ExternalBeginFrameSource,
-                                 cc::ExternalBeginFrameSourceClient {
+class CONTENT_EXPORT GpuVSyncBeginFrameSource
+    : public cc::ExternalBeginFrameSource,
+      cc::ExternalBeginFrameSourceClient {

[sunnyps, 2017/05/30 22:13:17]

nit: public cc::ExternalBeginFrameSourceClient

[stanisc, 2017/05/31 01:17:53]

This inheritance doesn't need to be public because users of
GpuVSyncBeginFrameSource don't need to see
ExternalBeginFrameSourceClient::OnNeedsBeginFrames or even know that
GpuVSyncBeginFrameSource derives from that class.

[sunnyps, 2017/05/31 01:26:02]

google style guide prohibits private inheritance:
https://google.github.io/styleguide/cppguide.html#Inheritance

[stanisc, 2017/05/31 17:33:12]

Thanks to pointing out to that! Done.

  public:
   explicit GpuVSyncBeginFrameSource(GpuVSyncControl* vsync_control);
   ~GpuVSyncBeginFrameSource() override;
 
   // cc::ExternalBeginFrameSourceClient implementation.
   void OnNeedsBeginFrames(bool needs_begin_frames) override;
 
   void OnVSync(base::TimeTicks timestamp, base::TimeDelta interval);
 
+ protected:
+  // Virtual for testing.
+  virtual base::TimeTicks Now() const;
+
  private:
+  bool GetMissedBeginFrameArgs(cc::BeginFrameObserver* obs,
+                               cc::BeginFrameArgs* missed_args) override;
+
   GpuVSyncControl* const vsync_control_;
   bool needs_begin_frames_;
   uint64_t next_sequence_number_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuVSyncBeginFrameSource);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_COMPOSITOR_GPU_VSYNC_BEGIN_FRAME_SOURCE_H_