Prevent Control+two-finger-scroll from zooming the page.

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/debug/trace_event.h"
@@ skipping 1205 matching lines @@
     const blink::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 & blink::WebInputEvent::ControlKey)) {
+      (event.modifiers & blink::WebInputEvent::ControlKey) &&
+      // Avoid adjusting the zoom in response to two-finger-scrolling touchpad
+      // gestures, which are regrettably easy to trigger accidentally.
+      !event.hasPreciseScrollingDeltas) {
     delegate_->ContentsZoomChange(event.wheelTicksY > 0);
     return true;
   }
 #endif
   return false;
 }
 
 bool WebContentsImpl::PreHandleGestureEvent(
     const blink::WebGestureEvent& event) {
   return delegate_ && delegate_->PreHandleGestureEvent(this, event);
@@ skipping 2644 matching lines @@
 
 void WebContentsImpl::OnPreferredSizeChanged(const gfx::Size& old_size) {
   if (!delegate_)
     return;
   const gfx::Size new_size = GetPreferredSize();
   if (new_size != old_size)
     delegate_->UpdatePreferredSize(this, new_size);
 }
 
 }  // namespace content