Give blink a chance to consume ctrl+wheel events before 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/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "content/renderer/input/input_handler_proxy_client.h"
@@ skipping 97 matching lines @@
   DCHECK(input_handler_);
 
   if (event.type == WebInputEvent::MouseWheel) {
     const WebMouseWheelEvent& wheel_event =
         *static_cast<const WebMouseWheelEvent*>(&event);
     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
       return DID_NOT_HANDLE;
     }
+    if (wheel_event.modifiers & WebInputEvent::ControlKey) {
+      // Wheel events involving the control key never trigger scrolling, only
+      // event handlers.  Forward to the main thread.
+      return DID_NOT_HANDLE;
+    }
     cc::InputHandler::ScrollStatus scroll_status = input_handler_->ScrollBegin(
         gfx::Point(wheel_event.x, wheel_event.y), cc::InputHandler::Wheel);
     switch (scroll_status) {
       case cc::InputHandler::ScrollStarted: {
         TRACE_EVENT_INSTANT2(
             "renderer",
             "InputHandlerProxy::handle_input wheel scroll",
             TRACE_EVENT_SCOPE_THREAD,
             "deltaX",
             -wheel_event.deltaX,
@@ skipping 353 matching lines @@
   TRACE_EVENT2("renderer",
                "InputHandlerProxy::notifyCurrentFlingVelocity",
                "vx",
                velocity.width,
                "vy",
                velocity.height);
   input_handler_->NotifyCurrentFlingVelocity(ToClientScrollIncrement(velocity));
 }
 
 }  // namespace content