Early terminate flings when scrolling impossible

public/platform/WebGestureCurveTarget.h

Index: public/platform/WebGestureCurveTarget.h
diff --git a/public/platform/WebGestureCurveTarget.h b/public/platform/WebGestureCurveTarget.h
index 5433387992e0bc9a7ef887b97d9e10e4de65aad7..a3c3338ebe494b5f5a2f8cc0a9abeaa0021d0034 100644
--- a/public/platform/WebGestureCurveTarget.h
+++ b/public/platform/WebGestureCurveTarget.h
@@ -32,9 +32,14 @@ namespace blink {
 
 class WebGestureCurveTarget {
 public:
-    virtual void scrollBy(const WebFloatSize& delta) = 0;
+    // TODO(jdduke): Make pure virtual when crrev.com/136173004 lands.
+    virtual bool scrollBy(const WebFloatSize& delta, const WebFloatSize& velocity) { return false; }
 
-    virtual void notifyCurrentFlingVelocity(const WebFloatSize&) { }
+    // TODO(jdduke): Remove when crrev.com/136173004 lands.
+    virtual void scrollBy(const WebFloatSize& delta) { }
+
+    // TODO(jdduke): Remove when crrev.com/136173004 lands.
+    virtual void notifyCurrentFlingVelocity(const WebFloatSize& velocity) { }
 
 protected:
     virtual ~WebGestureCurveTarget() { }