Add DidSaveScrollOrScaleState flag to prevent restoreScrollPositionAndViewState restore from default

third_party/WebKit/Source/core/loader/FrameLoader.cpp

Index: third_party/WebKit/Source/core/loader/FrameLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/FrameLoader.cpp b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
index 26bd2f95c92e404ed37be2e1c80177c58efb2a69..dac54ee3be826c57af7b4498f55757603b286852 100644
--- a/third_party/WebKit/Source/core/loader/FrameLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
@@ -284,6 +284,7 @@ void FrameLoader::saveScrollState() {
   if (m_frame->isMainFrame())
     m_currentItem->setPageScaleFactor(m_frame->page()->pageScaleFactor());
 
+  m_currentItem->setDidSaveScrollState(true);

[majidvp, 2017/02/14 20:42:17]

should we set this flag inside HistoryItem::setScrollOffset and
HistoryItem::setVisualViewportScrollOffset instead of here. That way we never
risk setting the value but not the flag.

   client()->didUpdateCurrentHistoryItem();
 }
 
@@ -421,6 +422,7 @@ void FrameLoader::setHistoryItemStateForCommit(
     return;
   m_currentItem->setDocumentSequenceNumber(oldItem->documentSequenceNumber());
   m_currentItem->setScrollOffset(oldItem->getScrollOffset());
+  m_currentItem->setDidSaveScrollState(oldItem->didSaveScrollState());

[majidvp, 2017/02/14 20:42:17]

Perhaps copy over the scroll state only if the didSaveScrollState is true?

   m_currentItem->setVisualViewportScrollOffset(
       oldItem->visualViewportScrollOffset());
   m_currentItem->setPageScaleFactor(oldItem->pageScaleFactor());
@@ -1414,6 +1416,8 @@ void FrameLoader::restoreScrollPositionAndViewStateForLoadType(
   }
   if (!needsHistoryItemRestore(loadType))
     return;
+  if (!m_currentItem->didSaveScrollState())
+    return;
 
   bool shouldRestoreScroll =
       m_currentItem->scrollRestorationType() != ScrollRestorationManual;