New flingCancel flag to prevent fling boosting.

public/web/WebInputEvent.h

Index: public/web/WebInputEvent.h
diff --git a/public/web/WebInputEvent.h b/public/web/WebInputEvent.h
index 20d4785044c950bebc586ddb37100ed00def649b..172d15c9b92bb6779f13afe832bd42d3ee20781e 100644
--- a/public/web/WebInputEvent.h
+++ b/public/web/WebInputEvent.h
@@ -468,6 +468,12 @@ public:
         } flingStart;
 
         struct {
+            // If set to true, don't treat flingCancel
+            // as a part of fling boost events sequence.
+            bool preventBoosting;
+        } flingCancel;
+
+        struct {
             float scale;
         } pinchUpdate;
     } data;