Explicitly suppress scrolling for wheel events that will trigger zooming

content/browser/renderer_host/web_input_event_aura.cc

Index: content/browser/renderer_host/web_input_event_aura.cc
diff --git a/content/browser/renderer_host/web_input_event_aura.cc b/content/browser/renderer_host/web_input_event_aura.cc
index 7dfbd9a184ba80ad9d188ab73f01c61fc3d05476..97698b821e680f62a967f66178bce4a490c021e7 100644
--- a/content/browser/renderer_host/web_input_event_aura.cc
+++ b/content/browser/renderer_host/web_input_event_aura.cc
@@ -198,6 +198,14 @@ blink::WebMouseWheelEvent MakeWebMouseWheelEvent(
   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;
 }