Ignore redundant calls to ScrollAnchor::save.

third_party/WebKit/Source/core/layout/ScrollAnchor.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ScrollAnchor_h
 #define ScrollAnchor_h
 
 #include "core/CoreExport.h"
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/heap/Handle.h"
@@ skipping 92 matching lines @@
 
     // Location of m_layoutObject relative to scroller at time of save().
     LayoutPoint m_savedRelativeOffset;
 
     // We suppress scroll anchoring after a style change on the anchor node or
     // one of its ancestors, if that change might have caused the node to move.
     // This bit tracks whether we have had a scroll-anchor-disabling style
     // change since the last layout.  It is recomputed in save(), and used to
     // suppress the adjustment in restore().  More at http://bit.ly/sanaclap.
     bool m_scrollAnchorDisablingStyleChanged;
+
+    // True iff save has been called, and restore has not been called since
+    // the call to save.  (In this state, additional calls to save are ignored.)
+    bool m_saved;

[ojan, 2016/09/01 05:39:48]

Might be nice to explain that this is to deal with multi-pass layout and to have
a TODO to explore changing scroll anchoring to be at frame boundaries and
removing this bool.

[skobes, 2016/09/01 20:47:21]

Done.

 };
 
 } // namespace blink
 
 #endif // ScrollAnchor_h