Prevent ctrl+2f scroll on the touchpad to zoom the page

content/browser/renderer_host/render_widget_host_view_aura.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/renderer_host/render_widget_host_view_aura.h"
 
 #include "base/auto_reset.h"
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/callback_helpers.h"
@@ skipping 2847 matching lines @@
     return;
 
   if (event->type() == ui::ET_SCROLL) {
     if (event->finger_count() != 2)
       return;
     blink::WebGestureEvent gesture_event =
         MakeWebGestureEventFlingCancel();
     host_->ForwardGestureEvent(gesture_event);
     blink::WebMouseWheelEvent mouse_wheel_event =
         MakeWebMouseWheelEvent(event);
+
+    // We don't want ctrl+two finger scroll to trigger the WebContents zooming
+    // function as it is too sensitive and most people don't expect the effect
+    // (unlike ctrl+mousewheel, which most people expect to zoom the page).
+    // Therefore, we clear the modifier here if and only if the ctrl key is
+    // pressed and no any other key is pressed at the same time. This prevents
+    // WebContentsImpl from zooming the page while retaining the scroll event
+    // and other modifier combinations in case the webpage might want to use
+    // them.
+    if (mouse_wheel_event.modifiers == blink::WebInputEvent::ControlKey)
+      mouse_wheel_event.modifiers = 0;

[sadrul, 2014/01/03 18:09:17]

If we want to disable this only on chromeos, then this is a reasonable fix
(since we create ui::ScrollEvent only on chromeos). But if we want to do this on
other platforms, then this change should be elsewhere. I have left a comment on
the bug asking about this.

[Rick Byers, 2014/04/04 17:35:53]

I think it's fine to do this for ChromeOS only for now.  The problem is really
specific to each OS (each have a different way of communicating this and
different sensitivity etc.).  I suggest we land it this way for now, and I can
tweak the Mac and Windows behavior as necessary as part of
http://crbug.com/289887.

[sadrul, 2014/04/04 19:00:21]

Note that shortly after this patchset, we started generating scroll events on
Windows too (https://codereview.chromium.org/133053004/).

     host_->ForwardWheelEvent(mouse_wheel_event);
     RecordAction(UserMetricsAction("TrackpadScroll"));
   } else if (event->type() == ui::ET_SCROLL_FLING_START ||
              event->type() == ui::ET_SCROLL_FLING_CANCEL) {
     blink::WebGestureEvent gesture_event =
         MakeWebGestureEvent(event);
     host_->ForwardGestureEvent(gesture_event);
     if (event->type() == ui::ET_SCROLL_FLING_START)
       RecordAction(UserMetricsAction("TrackpadScrollFling"));
   }
@@ skipping 608 matching lines @@
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void RenderWidgetHostViewPort::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content