Don't spam the log for gesture events

We don't convert all the gesture events to WebInputEvents. We don't need to
spam the log about it.

R=ojan@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/877733004

viewer/converters/input_event_types.cc

@@ -158,7 +158,6 @@ scoped_ptr<blink::WebInputEvent> BuildWebGestureEvent(
           event->gesture_data->scale / device_pixel_ratio;
       break;
     default:
-      NOTIMPLEMENTED() << "Received unexpected event: " << event->action;
       break;
   }