use enum to specify deviceSource for fling animation.

content/common/input/synthetic_web_input_event_builders.h

Index: content/common/input/synthetic_web_input_event_builders.h
diff --git a/content/common/input/synthetic_web_input_event_builders.h b/content/common/input/synthetic_web_input_event_builders.h
index 33442519005696f4789e9328c74a9020194a45cf..f16830d2cba00819029df74c7b7aa1c2fc651002 100644
--- a/content/common/input/synthetic_web_input_event_builders.h
+++ b/content/common/input/synthetic_web_input_event_builders.h
@@ -39,9 +39,8 @@ class CONTENT_EXPORT SyntheticWebKeyboardEventBuilder {
 
 class CONTENT_EXPORT SyntheticWebGestureEventBuilder {
  public:
-  static blink::WebGestureEvent Build(
-      blink::WebInputEvent::Type type,
-      blink::WebGestureEvent::SourceDevice source_device);
+  static blink::WebGestureEvent Build(blink::WebInputEvent::Type type,
+                                      blink::WebGestureDevice source_device);
   static blink::WebGestureEvent BuildScrollBegin(float dx_hint,
                                                  float dy_hint);
   static blink::WebGestureEvent BuildScrollUpdate(float dx,
@@ -52,11 +51,11 @@ class CONTENT_EXPORT SyntheticWebGestureEventBuilder {
       float anchor_x,
       float anchor_y,
       int modifiers,
-      blink::WebGestureEvent::SourceDevice source_device);
+      blink::WebGestureDevice source_device);
   static blink::WebGestureEvent BuildFling(
       float velocity_x,
       float velocity_y,
-      blink::WebGestureEvent::SourceDevice source_device);
+      blink::WebGestureDevice source_device);
 };
 
 class CONTENT_EXPORT SyntheticWebTouchEvent