Plumb gesture source value through Blink.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index 27b2257ce476d635243430b6c24a9933cf7077e6..6e8a92d3298df06075f541c4339ba5a4f99bb4fb 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -1874,7 +1874,7 @@ void WebViewImpl::beginFrame(const WebBeginFrameArgs& frameTime)
 
             PlatformGestureEvent endScrollEvent(PlatformEvent::GestureScrollEnd,
                 m_positionOnFlingStart, m_globalPositionOnFlingStart,
-                IntSize(), 0, PlatformEvent::NoModifiers);
+                IntSize(), 0, PlatformEvent::NoModifiers, PlatformGestureSourceUninitialized);

[tdresser, 2015/10/14 15:14:20]

Uninitialized doesn't feel quite right here. It might be better to keep track of
what device caused the fling.

[wjmaclean, 2015/10/14 15:55:09]

Done.

Turns out WebViewImpl already had a var for this, though I had to convert it
from bool :-/

             endScrollEvent.setScrollGestureData(0, 0, 0, 0, true, false, -1 /* null plugin id */);
 
             mainFrameImpl()->frame()->eventHandler().handleGestureScrollEnd(endScrollEvent);