Ignore redundant calls to ScrollAnchor::save.

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

 // 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.
 
 #include "core/layout/ScrollAnchor.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/UseCounter.h"
 #include "core/layout/line/InlineTextBox.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "platform/Histogram.h"
 
 namespace blink {
 
 using Corner = ScrollAnchor::Corner;
 
 ScrollAnchor::ScrollAnchor()
     : m_anchorObject(nullptr)
     , m_corner(Corner::TopLeft)
     , m_scrollAnchorDisablingStyleChanged(false)
+    , m_saved(false)
 {
 }
 
 ScrollAnchor::ScrollAnchor(ScrollableArea* scroller)
     : ScrollAnchor()
 {
     setScroller(scroller);
 }
 
 ScrollAnchor::~ScrollAnchor()
@@ skipping 167 matching lines @@
         if (current->scrollAnchorDisablingStyleChanged())
             return true;
         if (current == scrollerBox)
             return false;
         current = current->parent();
     }
 }
 
 void ScrollAnchor::save()
 {
+    if (m_saved)
+        return;
+    m_saved = true;
     DCHECK(m_scroller);
     if (m_scroller->scrollPosition() == IntPoint::zero()) {
         clear();
         return;
     }
 
     if (!m_anchorObject) {
         findAnchor();
         if (!m_anchorObject)
             return;
@@ skipping 17 matching lines @@
     // anchor node may round differently from the snapping of the scroll position.
     // (For example, anchor moving from 2.4px -> 2.6px is really 2px -> 3px, so we
     // should scroll by 1px instead of 0.2px.) This is true regardless of whether
     // the ScrollableArea actually uses fractional scroll positions.
     return roundedIntSize(computeRelativeOffset(m_anchorObject, m_scroller, m_corner)) -
         roundedIntSize(m_savedRelativeOffset);
 }
 
 void ScrollAnchor::restore()
 {
+    if (!m_saved)
+        return;
+    m_saved = false;
     DCHECK(m_scroller);
     if (!m_anchorObject)
         return;
     IntSize adjustment = computeAdjustment();
     if (adjustment.isZero())
         return;
 
     if (m_scrollAnchorDisablingStyleChanged) {
         // Note that we only clear if the adjustment would have been non-zero.
         // This minimizes redundant calls to findAnchor.
@@ skipping 25 matching lines @@
     return m_anchorObject == layoutObject;
 }
 
 void ScrollAnchor::notifyRemoved(LayoutObject* layoutObject)
 {
     if (m_anchorObject == layoutObject)
         clear();
 }
 
 } // namespace blink