Ignore redundant calls to ScrollAnchor::save.

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

Index: third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
diff --git a/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp b/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
index ab410d2abc6c85373c9454a0b08cadb12a36eb5d..30bddb2c55b925b7640db234be90d847f0b376ec 100644
--- a/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
+++ b/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
@@ -18,6 +18,7 @@ ScrollAnchor::ScrollAnchor()
     : m_anchorObject(nullptr)
     , m_corner(Corner::TopLeft)
     , m_scrollAnchorDisablingStyleChanged(false)
+    , m_saved(false)
 {
 }
 
@@ -205,6 +206,9 @@ bool ScrollAnchor::computeScrollAnchorDisablingStyleChanged()
 
 void ScrollAnchor::save()
 {
+    if (m_saved)
+        return;
+    m_saved = true;
     DCHECK(m_scroller);
     if (m_scroller->scrollPosition() == IntPoint::zero()) {
         clear();
@@ -242,6 +246,7 @@ IntSize ScrollAnchor::computeAdjustment() const
 
 void ScrollAnchor::restore()
 {
+    m_saved = false;

[ymalik, 2016/09/01 14:13:04]

Add a DCHECK that m_saved is true? We should never be calling restore without
save right? 

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

I tried this, but it breaks tests due to nested FrameView layouts, and due to
the use of restore from PLSA::clampScrollPositionsAfterLayout (for scenarios
that don't involve DelayScrollPositionClampScope).

Instead I've added an early return in restore() to parallel the early return in
save().

     DCHECK(m_scroller);
     if (!m_anchorObject)
         return;