Explicitly suppress scrolling for wheel events that will trigger zooming

content/browser/renderer_host/input/input_router_impl.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/browser/renderer_host/input/input_router_impl.h"
 
 #include <math.h>
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
@@ skipping 439 matching lines @@
   //  - magnitude roughly matches wheels: f(2) > 25 && f(2) < 100
   //  - a formula that's relatively easy to use from JavaScript
   // Note that 'wheel' event deltaY values have their sign inverted.  So to
   // convert a wheel deltaY back to a scale use Math.exp(-deltaY/100).
   DCHECK_GT(pinch_event.event.data.pinchUpdate.scale, 0);
   wheelEvent.deltaY = 100.0f * log(pinch_event.event.data.pinchUpdate.scale);
   wheelEvent.hasPreciseScrollingDeltas = true;
   wheelEvent.wheelTicksX = 0;
   wheelEvent.wheelTicksY =
       pinch_event.event.data.pinchUpdate.scale > 1 ? 1 : -1;
-
+  // Avoid touchpad pinch on Mac OS to scroll.

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

Is this Mac OS specific?

Reword to:
Prevent trackpad pinch from scrolling.
OR
Prevent trackpad pinch from scrolling on Mac OS.

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

Done.

Yes, this is only for Mac OS.

+  wheelEvent.canScroll = false;
   SendWheelEvent(QueuedWheelEvent(
       MouseWheelEventWithLatencyInfo(wheelEvent, pinch_event.latency), true));
 }
 
 void InputRouterImpl::OnInputEventAck(
     const InputHostMsg_HandleInputEvent_ACK_Params& ack) {
   client_->DecrementInFlightEventCount();
 
   // Log the time delta for processing an input event.
   TimeDelta delta = TimeTicks::Now() - input_event_start_time_;
@@ skipping 240 matching lines @@
 InputRouterImpl::QueuedWheelEvent::QueuedWheelEvent(
     const MouseWheelEventWithLatencyInfo& event,
     bool synthesized_from_pinch)
     : event(event), synthesized_from_pinch(synthesized_from_pinch) {
 }
 
 InputRouterImpl::QueuedWheelEvent::~QueuedWheelEvent() {
 }
 
 }  // namespace content