Handle mac trackpad zoom via GesturePinch events

content/browser/renderer_host/input/input_router_impl.cc

Index: content/browser/renderer_host/input/input_router_impl.cc
diff --git a/content/browser/renderer_host/input/input_router_impl.cc b/content/browser/renderer_host/input/input_router_impl.cc
index 105051105bb1a7f5bff2551a063bec41ba313a65..1a9e1c91d08fcbf92467e58d41b48eec508a05ce 100644
--- a/content/browser/renderer_host/input/input_router_impl.cc
+++ b/content/browser/renderer_host/input/input_router_impl.cc
@@ -242,6 +242,16 @@ void InputRouterImpl::SendGestureEvent(
     const GestureEventWithLatencyInfo& original_gesture_event) {
   event_stream_validator_.OnEvent(original_gesture_event.event);
   GestureEventWithLatencyInfo gesture_event(original_gesture_event);
+
+  // Trackpad pinch gestures are not yet handled by the renderer.
+  // TODO(rbyers): Send mousewheel for trackpad pinch - crbug.com/289887.
+  if (gesture_event.event.sourceDevice == WebGestureEvent::Touchpad &&

[jdduke (slow), 2014/03/26 23:13:43]

I always hesitate to ack an event out-of-order.  Would it kill us to ack the
pinch *after* it's passed through the GEQ just before it's to be sent to the
renderer?  

Hmm, actually, a (perhaps better) alternative here would be to leverage the
|RenderWidgetHostView*::FilterInputEvent()| method, in this case we would have
|RenderWidgetHostViewMac| intercept the pinch and return
INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS, and we wouldn't need to touch anything
here in the router.

[Rick Byers, 2014/03/27 01:44:09]

Yeah that's probably better - done.
My next CL will involve turning these gestures into ctrl+mousewheel events, and
I _think_ the InputRouter (somewhere) is probably the right place to do that. 
In particular I'm going to need to hook things up so that when the SPECIFIC
wheel event ACK comes back from the renderer, it results in an ACK being sent
for the GesturePinchUpdate.  I haven't figured out exactly how I'm going to do
this yet, but I think it'll involve changes here.  So I'd rather land this CL
like this, then we can debate exactly that structure in the next CL (probably in
a week or two after I get through some other things).  Sound good?

+      (gesture_event.event.type == WebInputEvent::GesturePinchUpdate)) {
+    ack_handler_->OnGestureEventAck(gesture_event,
+        INPUT_EVENT_ACK_STATE_NOT_CONSUMED);
+    return;
+  }
+
   if (touch_action_filter_.FilterGestureEvent(&gesture_event.event))
     return;