Add a completion callback to gpuBenchmarking.beginSmoothScroll

content/port/browser/smooth_scroll_gesture.h

Index: content/port/browser/smooth_scroll_gesture.h
diff --git a/content/port/browser/smooth_scroll_gesture.h b/content/port/browser/smooth_scroll_gesture.h
index 6d6672cbd26b87d0664ea4b4f52954b429f774be..4e2c1d908f411e0e6d63b49c6e96798d7f86b665 100644
--- a/content/port/browser/smooth_scroll_gesture.h
+++ b/content/port/browser/smooth_scroll_gesture.h
@@ -5,6 +5,7 @@
 #ifndef CONTENT_PORT_BROWSER_SMOOTH_SCROLL_GESTURE_H_
 #define CONTENT_PORT_BROWSER_SMOOTH_SCROLL_GESTURE_H_
 
+#include "base/memory/ref_counted.h"
 #include "base/time.h"
 
 namespace content {
@@ -14,9 +15,8 @@ class RenderWidgetHost;
 // This is a base class representing a single scroll gesture. These gestures are
 // paired with the rendering benchmarking system to (automatically) measure how
 // smoothnly chrome is responding to user input.
-class SmoothScrollGesture {
+class SmoothScrollGesture : public base::RefCounted<SmoothScrollGesture> {
  public:
-  virtual ~SmoothScrollGesture() {}
 
   // When called, the gesture should compute its state at the provided timestamp
   // and send the right input events to the provided RenderWidgetHost to
@@ -26,6 +26,9 @@ class SmoothScrollGesture {
   // value will stop ticking the gesture and clean it up.
   virtual bool ForwardInputEvents(base::TimeTicks now,
                                   RenderWidgetHost* host) = 0;
+ protected:
+  friend class base::RefCounted<SmoothScrollGesture>;
+  virtual ~SmoothScrollGesture() {}
 };
 
 } // namespace content