Plumb gesture source value through Blink.

content/common/input/gesture_event_stream_validator.cc

Index: content/common/input/gesture_event_stream_validator.cc
diff --git a/content/common/input/gesture_event_stream_validator.cc b/content/common/input/gesture_event_stream_validator.cc
index 6ea29de25ac8536fd054b45af307ee58dc5cdebe..0633bd385f83923e75d8b5b5d5e5e5ecdfd2bde6 100644
--- a/content/common/input/gesture_event_stream_validator.cc
+++ b/content/common/input/gesture_event_stream_validator.cc
@@ -100,6 +100,15 @@ bool GestureEventStreamValidator::Validate(const blink::WebGestureEvent& event,
     default:
       break;
   }
+  // TODO(wjmaclean): At some future point we may wish to consider adding a
+  // 'continuity check', requiring that all events between an initial tap-down
+  // and whatever terminates the sequence to have the same source device type.
+  if (event.sourceDevice == blink::WebGestureDeviceTouchpad &&
+      !WebInputEvent::isGestureScrollEventType(event.type)) {
+    error_msg->append(

[jdduke (slow), 2015/10/19 18:15:38]

Hmm, I was thinking something even more basic, like

if (event.sourceDevice == blink::WebGestureDeviceUninitialized)
  error_msg->append("Gesture event source is uninitialized.\n");

The touchpad validation can probably happen in a separate patch? Maybe Tim can
follow up on that as it's somewhat orthogonal to the issue at hand.

[wjmaclean, 2015/10/19 18:58:49]

Done.

+        "Touchpad device should only be used for scroll events.\n");
+  }
+
   return error_msg->empty();
 }