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 4fe79c16dd1aae6893132ca789bc567c5449fa50..50dcc0226f77cb7a4dd0306b980cf049b0d6bcb7 100644
--- a/content/browser/renderer_host/web_input_event_aura.cc
+++ b/content/browser/renderer_host/web_input_event_aura.cc
@@ -197,6 +197,14 @@ blink::WebMouseWheelEvent MakeWebMouseWheelEvent(ui::MouseWheelEvent* event) {
   webkit_event.globalX = root_point.x();
   webkit_event.globalY = root_point.y();
 
+  // Avoid adjusting the zoom in response to two-finger-scrolling touchpad
+  // gestures. We're enabling WebContentsImpl::HandleWheelEvent to use the
+  // event to zoom the page when MouseWheelEvent does not scroll.

[tdresser, 2014/12/02 15:37:38]

Can you clarify this?

Perhaps assign hasPreciseScrollingDeltas to a local bool fromMouseWheel or
fromTrackpad?

I don't think you need to explicitly reference WebContentsImpl here.
Say something more along the lines of:
"Scroll events generated from the mouse wheel when the control key is held don't
trigger scrolling. Instead, they may cause zooming."

[lanwei, 2014/12/02 22:28:06]

Done.

+  if ((webkit_event.modifiers & blink::WebInputEvent::ControlKey)
+      && !webkit_event.hasPreciseScrollingDeltas) {
+    webkit_event.canScroll = false;
+  }
+
   return webkit_event;
 }