[Merge to M59] Re-add delay to PostTask in StartScrollbarPaintTimer()

third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm

 /*
  * Copyright (C) 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1013 matching lines @@
   // page cache, and
   // a relayout will happen on its own. Otherwise, we must initiate a re-layout
   // ourselves.
   if (!needs_scroller_style_update_)
     GetScrollableArea()->ScrollbarStyleChanged();
 
   needs_scroller_style_update_ = false;
 }
 
 void ScrollAnimatorMac::StartScrollbarPaintTimer() {
-  initial_scrollbar_paint_task_handle_ = task_runner_->PostCancellableTask(
-      BLINK_FROM_HERE, WTF::Bind(&ScrollAnimatorMac::InitialScrollbarPaintTask,
-                                 WrapWeakPersistent(this)));
+  // Post a task with 1 ms delay to give a chance to run other immediate tasks
+  // that may cancel this.
+  initial_scrollbar_paint_task_handle_ =
+      task_runner_->PostDelayedCancellableTask(
+          BLINK_FROM_HERE,
+          WTF::Bind(&ScrollAnimatorMac::InitialScrollbarPaintTask,
+                    WrapWeakPersistent(this)),
+          1);
 }
 
 bool ScrollAnimatorMac::ScrollbarPaintTimerIsActive() const {
   return initial_scrollbar_paint_task_handle_.IsActive();
 }
 
 void ScrollAnimatorMac::StopScrollbarPaintTimer() {
   initial_scrollbar_paint_task_handle_.Cancel();
 }
 
@@ skipping 34 matching lines @@
     rect_in_view_coordinates =
         vertical_scrollbar->ConvertToContainingFrameViewBase(scroller_thumb);
 
   if (rect_in_view_coordinates == visible_scroller_thumb_rect_)
     return;
 
   visible_scroller_thumb_rect_ = rect_in_view_coordinates;
 }
 
 }  // namespace blink