Fix smooth scroll jump when switching scroll handling between MT and CC

third_party/WebKit/public/platform/WebLayer.h

Index: third_party/WebKit/public/platform/WebLayer.h
diff --git a/third_party/WebKit/public/platform/WebLayer.h b/third_party/WebKit/public/platform/WebLayer.h
index ff846d5bf65197f1550bda59cedff32fb2f82c16..51c8619d42f8237e935357315b6bea33a789d02a 100644
--- a/third_party/WebKit/public/platform/WebLayer.h
+++ b/third_party/WebKit/public/platform/WebLayer.h
@@ -201,8 +201,8 @@ public:
 
     // Indicates that this layer will always scroll on the main thread for the provided reason.
     virtual void addMainThreadScrollingReasons(uint32_t) = 0;
-    // Indicates that the layer could scroll on the compositor thread.
-    virtual void clearMainThreadScrollingReasons() = 0;
+    virtual void clearMainThreadScrollingReasons(uint32_t mainThreadScrollingReasonsToClear) = 0;
+    virtual uint32_t mainThreadScrollingReasons() = 0;
     virtual bool shouldScrollOnMainThread() const = 0;
 
     virtual void setNonFastScrollableRegion(const WebVector<WebRect>&) = 0;