Explicitly suppress scrolling for wheel events that will trigger zooming

content/renderer/input/input_handler_proxy.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/input/input_handler_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 275 matching lines @@
 
 InputHandlerProxy::EventDisposition InputHandlerProxy::HandleMouseWheel(
     const WebMouseWheelEvent& wheel_event) {
   InputHandlerProxy::EventDisposition result = DID_NOT_HANDLE;
   cc::InputHandlerScrollResult scroll_result;
 
   if (wheel_event.scrollByPage) {
     // TODO(jamesr): We don't properly handle scroll by page in the compositor
     // thread, so punt it to the main thread. http://crbug.com/236639
     result = DID_NOT_HANDLE;
-  } else if (wheel_event.modifiers & WebInputEvent::ControlKey) {
-    // Wheel events involving the control key never trigger scrolling, only
-    // event handlers.  Forward to the main thread.
+  } else if (!wheel_event.canScroll) {
+    // Wheel events involving the control key with canScroll false will not

[tdresser, 2014/12/02 15:37:38]

I don't think you need to reference both the control key and |canScroll|. 

I'd say something like:
// Wheel events with |canScroll| == false will not trigger scrolling, ....

[lanwei, 2014/12/02 22:28:06]

Done.

+    // trigger scrolling, only event handlers.  Forward to the main thread.
     result = DID_NOT_HANDLE;
   } else if (smooth_scroll_enabled_) {
     cc::InputHandler::ScrollStatus scroll_status =
         input_handler_->ScrollAnimated(
             gfx::Point(wheel_event.x, wheel_event.y),
             gfx::Vector2dF(-wheel_event.deltaX, -wheel_event.deltaY));
     switch (scroll_status) {
       case cc::InputHandler::ScrollStarted:
         result = DID_HANDLE;
         break;
@@ skipping 578 matching lines @@
   // trigger a scroll, e.g., with a trivial time delta between fling updates.
   // Return true in this case to prevent early fling termination.
   if (std::abs(clipped_increment.width) < kScrollEpsilon &&
       std::abs(clipped_increment.height) < kScrollEpsilon)
     return true;
 
   return did_scroll;
 }
 
 }  // namespace content