Disable page zoom through control+scroll on Mac.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 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/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
@@ skipping 1218 matching lines @@
       delegate_->PreHandleKeyboardEvent(this, event, is_keyboard_shortcut);
 }
 
 void WebContentsImpl::HandleKeyboardEvent(const NativeWebKeyboardEvent& event) {
   if (delegate_)
     delegate_->HandleKeyboardEvent(this, event);
 }
 
 bool WebContentsImpl::PreHandleWheelEvent(
     const WebKit::WebMouseWheelEvent& event) {
+#if !defined(OS_MACOSX)
+  // On platforms other than Mac, control+mousewheel changes zoom. On Mac, this
+  // isn't done for two reasons:
+  //   -the OS already has a gesture to do this through pinch-zoom
+  //   -if a user starts an inertial scroll, let's go, and presses control
+  //      (i.e. control+tab) then the OS's buffered scroll events will come in
+  //      with control key set which isn't what the user wants
   if (delegate_ &&
       event.wheelTicksY &&
       (event.modifiers & WebKit::WebInputEvent::ControlKey)) {
     delegate_->ContentsZoomChange(event.wheelTicksY > 0);
     return true;
   }
+#endif
 
   return false;
 }
 
 void WebContentsImpl::HandleMouseMove() {
   if (delegate_) {
     delegate_->ContentsMouseEvent(
         this, gfx::Screen::GetNativeScreen()->GetCursorScreenPoint(), true);
   }
 }
@@ skipping 2151 matching lines @@
 }
 
 BrowserPluginGuestManager*
     WebContentsImpl::GetBrowserPluginGuestManager() const {
   return static_cast<BrowserPluginGuestManager*>(
       GetBrowserContext()->GetUserData(
           browser_plugin::kBrowserPluginGuestManagerKeyName));
 }
 
 }  // namespace content