Plumb gesture source value through Blink.

third_party/WebKit/public/web/WebInputEvent.h

Index: third_party/WebKit/public/web/WebInputEvent.h
diff --git a/third_party/WebKit/public/web/WebInputEvent.h b/third_party/WebKit/public/web/WebInputEvent.h
index 53ca6a160bca6f32f40af13023ef2e97fc2cefa4..9d61d87d775dfda12a788fb9c0249adc1fd5b0f1 100644
--- a/third_party/WebKit/public/web/WebInputEvent.h
+++ b/third_party/WebKit/public/web/WebInputEvent.h
@@ -113,6 +113,8 @@ public:
         KeyboardTypeLast = Char,
 
         // WebGestureEvent
+        // Note: Gesture scroll events (ScrollBegin ... FlingCancel) must be
+        //       kept sequential for isGestureScrollEventType() to work.
         GestureScrollBegin,
         GestureTypeFirst = GestureScrollBegin,
         GestureScrollEnd,
@@ -229,6 +231,12 @@ public:
         return GestureTypeFirst <= type && type <= GestureTypeLast;
     }
 
+    // Returns true if the WebInputEvent is a gesture scroll event.
+    static bool isGestureScrollEventType(int type)
+    {
+        return GestureScrollBegin <= type && type <= GestureFlingCancel;
+    }
+
 protected:
     explicit WebInputEvent(unsigned sizeParam)
     {
@@ -546,6 +554,7 @@ public:
         , y(0)
         , globalX(0)
         , globalY(0)
+        , sourceDevice(WebGestureDeviceUninitialized)
         , resendingPluginId(-1)
     {
         memset(&data, 0, sizeof(data));