Allow touch events to be uncancelable

public/web/WebInputEvent.h

Index: public/web/WebInputEvent.h
diff --git a/public/web/WebInputEvent.h b/public/web/WebInputEvent.h
index 78e33d89568b081b131fd5be51ed16f867a1c71b..c46d1fc8d29ff53c0a1cc721248f1e0120db4268 100644
--- a/public/web/WebInputEvent.h
+++ b/public/web/WebInputEvent.h
@@ -513,11 +513,17 @@ public:
     // List of all touches which are currently down and are targeting the event recipient.
     WebTouchPoint targetTouches[touchesLengthCap];
 
+    // Whether the event can be canceled (with preventDefault). If true then the browser
+    // must wait for an ACK for this event. If false then no ACK IPC is expected.
+    // See comment at the top for why an int is used here instead of a bool.
+    int cancelable;
+
     WebTouchEvent()
         : WebInputEvent(sizeof(WebTouchEvent))
         , touchesLength(0)
         , changedTouchesLength(0)
         , targetTouchesLength(0)
+        , cancelable(true)
     {
     }
 };