Move ScrollableArea timer to TaskRunnerTimer.

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
index 8c433da061fa448d30c7a4713ef06fb8648ed2e4..f5f6a86dd3463eda42ea8a71a86622a9c72d28ce 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
@@ -366,6 +366,10 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin {
 
   virtual void didScrollWithScrollbar(ScrollbarPart, ScrollbarOrientation) {}
 
+  // Returns the task runner to be used for scrollable area timers.
+  // Ideally a frame-specific throttled one can be used.
+  virtual RefPtr<WebTaskRunner> getTimerTaskRunner() const = 0;
+
  protected:
   ScrollableArea();
 
@@ -420,7 +424,7 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin {
   mutable Member<ScrollAnimatorBase> m_scrollAnimator;
   mutable Member<ProgrammaticScrollAnimator> m_programmaticScrollAnimator;
 
-  std::unique_ptr<Timer<ScrollableArea>> m_fadeOverlayScrollbarsTimer;
+  std::unique_ptr<TaskRunnerTimer<ScrollableArea>> m_fadeOverlayScrollbarsTimer;
 
   unsigned m_scrollbarOverlayColorTheme : 2;