Articulate the cancel behavior in the WebTouchEvent.

third_party/WebKit/Source/platform/PlatformEvent.h

Index: third_party/WebKit/Source/platform/PlatformEvent.h
diff --git a/third_party/WebKit/Source/platform/PlatformEvent.h b/third_party/WebKit/Source/platform/PlatformEvent.h
index 62b6cd29025e7d954a301869e6253e41b14578ae..752dd721828de911420104bb14d5b7349d9880ca 100644
--- a/third_party/WebKit/Source/platform/PlatformEvent.h
+++ b/third_party/WebKit/Source/platform/PlatformEvent.h
@@ -121,6 +121,16 @@ public:
         RailsModeVertical   = 2,
     };
 
+    enum DispatchType {
+        Blocking,
+        EventNonBlocking,
+        // All listeners are passive.
+        ListenersNonBlockingPassive,
+        // This value represents a state which would have normally blocking
+        // but was forced to be non-blocking.
+        ListenersForcedNonBlockingPassive,
+    };
+
     EventType type() const { return static_cast<EventType>(m_type); }
 
     bool shiftKey() const { return m_modifiers & ShiftKey; }