Implement Wheel Gesture Scrolling on OSX.

content/renderer/input/render_widget_input_handler.cc

Index: content/renderer/input/render_widget_input_handler.cc
diff --git a/content/renderer/input/render_widget_input_handler.cc b/content/renderer/input/render_widget_input_handler.cc
index e2f118fb9f9e56e2bca1533ef3f020c51228e9b6..22f02f6fb5604296e805cbfdbfb81fa29cb33afe 100644
--- a/content/renderer/input/render_widget_input_handler.cc
+++ b/content/renderer/input/render_widget_input_handler.cc
@@ -377,6 +377,18 @@ void RenderWidgetInputHandler::HandleInputEvent(
                            : gfx::Vector2dF(),
           processed != WebInputEventResult::NotHandled);
     }
+  } else if (input_event.type == WebInputEvent::GestureScrollBegin ||
+             input_event.type == WebInputEvent::GestureScrollEnd ||
+             input_event.type == WebInputEvent::GestureScrollUpdate) {
+    const WebGestureEvent& gesture_event =
+        static_cast<const WebGestureEvent&>(input_event);
+    if (gesture_event.sourceDevice == blink::WebGestureDeviceTouchpad) {
+      delegate_->ObserveGestureEventAndResult(
+          gesture_event,
+          event_overscroll ? event_overscroll->latest_overscroll_delta
+                           : gfx::Vector2dF(),
+          processed != WebInputEventResult::NotHandled);
+    }
   }
 
   bool frame_pending =