Honor the wheel event canScroll bit instead of trying to infer it from the ctrl modifier

Source/platform/scroll/ScrollableArea.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 221 matching lines @@
     else if (behaviorString == "smooth")
         behavior = ScrollBehaviorSmooth;
     else
         return false;
 
     return true;
 }
 
 bool ScrollableArea::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
 {
-    // ctrl+wheel events are used to trigger zooming, not scrolling.
-    if (wheelEvent.modifiers() & PlatformEvent::CtrlKey)
+    // Method suppressScroll() are used to trigger zooming, not scrolling.

[tdresser, 2014/11/27 15:06:09]

Reword to:

Wheel events whose scrolling has been suppressed are used to trigger zooming,
not scrolling.

[lanwei, 2014/12/02 15:48:10]

Done.

+    if (wheelEvent.suppressScroll())
         return false;
 
     cancelProgrammaticScrollAnimation();
     return scrollAnimator()->handleWheelEvent(wheelEvent);
 }
 
 // NOTE: Only called from Internals for testing.
 void ScrollableArea::setScrollOffsetFromInternals(const IntPoint& offset)
 {
     setScrollOffsetFromAnimation(DoublePoint(offset));
@@ skipping 229 matching lines @@
 {
     return scrollSize(orientation);
 }
 
 float ScrollableArea::pixelStep(ScrollbarOrientation) const
 {
     return 1;
 }
 
 } // namespace blink