Unify the calculation of main thread offset of sticky element

cc/blink/web_layer_impl.h

Index: cc/blink/web_layer_impl.h
diff --git a/cc/blink/web_layer_impl.h b/cc/blink/web_layer_impl.h
index 2cb948e42914e133a75e0e084e647302d510b125..ace68413b7a053e338f9dd6198c607e91bd48020 100644
--- a/cc/blink/web_layer_impl.h
+++ b/cc/blink/web_layer_impl.h
@@ -117,6 +117,8 @@ class CC_BLINK_EXPORT WebLayerImpl : public NON_EXPORTED_BASE(blink::WebLayer) {
       const blink::WebLayerStickyPositionConstraint& constraint) override;
   blink::WebLayerStickyPositionConstraint StickyPositionConstraint()
       const override;
+  void SetStickyMainThreadOffset(const blink::WebSize& offset) override;
+  blink::WebSize StickyMainThreadOffset() const override;
   void SetScrollClient(blink::WebLayerScrollClient* client) override;
   void SetLayerClient(cc::LayerClient* client) override;
   const cc::Layer* CcLayer() const override;