Move viewport actions into an ApplyScroll callback.

third_party/WebKit/Source/core/dom/Document.h

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index f130ef0e2c3852bfb8c4903318299438703f071c..ddc19640eeacd9becfcb717e3fead48c90ed33e8 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -1171,6 +1171,13 @@ private:
 
     const OriginAccessEntry& accessEntryFromURL();
 
+    // Installs the viewport scrolling callback (the "applyScroll" in Scroll
+    // Customization lingo) on the root scrollingElement. This callback is
+    // responsible for viewport related scroll actions like top controls
+    // movement and overscroll glow as well as actually scrolling the root
+    // viewport.
+    void updateViewportApplyScroll();
+
     DocumentLifecycle m_lifecycle;
 
     bool m_hasNodesWithPlaceholderStyle;
@@ -1277,6 +1284,10 @@ private:
 
     Member<Element> m_cssTarget;
 
+    // Not a WeakMember since we want to keep the scrollingElement around until
+    // we move its ApplyScroll onto the new scrollingElement.
+    Member<Element> m_oldScrollingElement;
+
     LoadEventProgress m_loadEventProgress;
 
     double m_startTime;