Explicitly suppress scrolling for wheel events that will trigger zooming

content/browser/renderer_host/web_input_event_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/web_input_event_aura.h"
 
 #include "content/browser/renderer_host/input/web_input_event_util.h"
 #include "content/browser/renderer_host/ui_events_helper.h"
 #include "ui/aura/window.h"
 #include "ui/events/event.h"
@@ skipping 180 matching lines @@
 
   // Replace the event's coordinate fields with translated position data from
   // |event|.
   webkit_event.windowX = webkit_event.x = event.x();
   webkit_event.windowY = webkit_event.y = event.y();
 
   const gfx::Point root_point = event.root_location();
   webkit_event.globalX = root_point.x();
   webkit_event.globalY = root_point.y();
 
+  // Scroll events generated from the mouse wheel when the control key is held
+  // don't trigger scrolling. Instead, they may cause zooming.
+  bool from_mouse_wheel = !webkit_event.hasPreciseScrollingDeltas;
+  if ((webkit_event.modifiers & blink::WebInputEvent::ControlKey) &&
+      from_mouse_wheel) {
+    webkit_event.canScroll = false;
+  }

[Rick Byers, 2014/12/12 22:20:29]

I think you could write a unit test for this code similar to the code in
RenderWidgetHostViewAuraTest::FinishCompositionByMouse.  I.e. construct a fake
Aura event, pass it to OnMouseEvent, then verify the canScroll bit in the
outgoing IPC message.

[lanwei, 2014/12/17 23:16:40]

Done.

+
   return webkit_event;
 }
 
 blink::WebMouseWheelEvent MakeWebMouseWheelEvent(const ui::ScrollEvent& event) {
 #if defined(OS_WIN)
   // Construct an untranslated event from the platform event data.
   blink::WebMouseWheelEvent webkit_event =
       MakeUntranslatedWebMouseWheelEventFromNativeEvent(event.native_event());
 #else
   blink::WebMouseWheelEvent webkit_event =
@@ skipping 143 matching lines @@
     webkit_event.deltaY = event.y_offset();
   }
 
   webkit_event.wheelTicksX = webkit_event.deltaX / kPixelsPerTick;
   webkit_event.wheelTicksY = webkit_event.deltaY / kPixelsPerTick;
 
   return webkit_event;
 }
 
 }  // namespace content