Plumb gesture source value through Blink.

content/common/input/gesture_event_stream_validator.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/input/gesture_event_stream_validator.h"
 
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "content/common/input/web_input_event_traits.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
@@ skipping 82 matching lines @@
       waiting_for_tap_end_ = false;
       break;
     case WebInputEvent::GestureDoubleTap:
       // DoubleTap gestures may be synthetically inserted, and do not require a
       // preceding TapDown.
       waiting_for_tap_end_ = false;
       break;
     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,
+  // and that touchpad gestures are only found on ScrollEvents.
+  if (event.sourceDevice == blink::WebGestureDeviceUninitialized)
+    error_msg->append("Gesture event source is uninitialized.\n");
+
   return error_msg->empty();
 }
 
 }  // namespace content