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

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index ad374246f96ac5d750fb9703868bb584f8262ff5..805992629e4040c2cf9b9c19d6fb5134297d931c 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -2514,6 +2514,18 @@ void RenderWidgetHostViewAura::OnScrollEvent(ui::ScrollEvent* event) {
     host_->ForwardGestureEvent(gesture_event);
     blink::WebMouseWheelEvent mouse_wheel_event =
         MakeWebMouseWheelEvent(event);
+
+    // We don't want Control+two-finger-scroll to trigger the WebContents
+    // zooming function as it is too sensitive and most people don't expect the
+    // effect (unlike Control+mouse-wheel, which is commonly used to zoom the
+    // page). Therefore, clear the modifier here if and only if the Control 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;

[Rick Byers, 2014/04/22 14:15:15]

Now that it's possible for pages to receive ctrl+wheel events
(http://crrev.com/254559) it seems a shame to strip the control modifier here.

Thinking about this more, I think the fundamental problem is that the zoom
handling in WebContentsImpl::HandleWheelEvent isn't designed for devices with
precise scroll deltas - the logic assumes there are fixed ticks.  See the
trackpad pinch handling in WebContentsImpl::HandleGestureEvent for an example of
similar logic that is designed for precise deltas.

So I think the right fix (for now) is to modify
WebContentsImpl::HandleWheelEvent to ignore wheel events with the
'hasPreciseDeltas' flag set.

[Daniel Erat, 2014/04/22 15:27:04]

thanks, makes sense (and i agree that it seems much better to handle this in the
place where we actually do the zooming)! i'll ping again after i've made this
change.

+
     host_->ForwardWheelEvent(mouse_wheel_event);
     RecordAction(base::UserMetricsAction("TrackpadScroll"));
   } else if (event->type() == ui::ET_SCROLL_FLING_START ||