Fix Omnibox.CharTypedToRepaintLatency regression with D3DVsync experiment

content/browser/compositor/gpu_vsync_begin_frame_source.h

Index: content/browser/compositor/gpu_vsync_begin_frame_source.h
diff --git a/content/browser/compositor/gpu_vsync_begin_frame_source.h b/content/browser/compositor/gpu_vsync_begin_frame_source.h
index a3ddd6b07863833b9d5bb2b267355db53dd4ed59..9df2f07d94010cd449ad5825f29b1936e2f952f7 100644
--- a/content/browser/compositor/gpu_vsync_begin_frame_source.h
+++ b/content/browser/compositor/gpu_vsync_begin_frame_source.h
@@ -8,19 +8,21 @@
 #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,
+      public cc::ExternalBeginFrameSourceClient {
  public:
   explicit GpuVSyncBeginFrameSource(GpuVSyncControl* vsync_control);
   ~GpuVSyncBeginFrameSource() override;
@@ -30,7 +32,14 @@ class GpuVSyncBeginFrameSource : public cc::ExternalBeginFrameSource,
 
   void OnVSync(base::TimeTicks timestamp, base::TimeDelta interval);
 
+ protected:
+  // Virtual for testing.
+  virtual base::TimeTicks Now() const;
+
  private:
+  cc::BeginFrameArgs GetMissedBeginFrameArgs(
+      cc::BeginFrameObserver* obs) override;
+
   GpuVSyncControl* const vsync_control_;
   bool needs_begin_frames_;
   uint64_t next_sequence_number_;