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.
+  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();
 }
 
 }  // namespace content