Add DidSaveScrollOrScaleState flag to prevent restoreScrollPositionAndViewState restore from default

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008 Alp Toker <alp@atoker.com>
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 Kris Jordan <krisjordan@gmail.com>
  * Copyright (C) 2011 Google Inc. All rights reserved.
@@ skipping 266 matching lines @@
 
   if (ScrollableArea* layoutScrollableArea =
           m_frame->view()->layoutViewportScrollableArea())
     m_currentItem->setScrollOffset(layoutScrollableArea->getScrollOffset());
   m_currentItem->setVisualViewportScrollOffset(toScrollOffset(
       m_frame->host()->visualViewport().visibleRect().location()));
 
   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();
 }
 
 void FrameLoader::dispatchUnloadEvent() {
   FrameNavigationDisabler navigationDisabler(*m_frame);
 
   // If the frame is unloading, the provisional loader should no longer be
   // protected. It will be detached soon.
   m_protectProvisionalLoader = false;
   saveScrollState();
@@ skipping 117 matching lines @@
   // Don't propagate state from the old item if this is a different-document
   // navigation, unless the before and after pages are logically related. This
   // means they have the same url (ignoring fragment) and the new item was
   // loaded via reload or client redirect.
   if (navigationType == HistoryNavigationType::DifferentDocument &&
       (historyCommitType != HistoryInertCommit ||
        !equalIgnoringFragmentIdentifier(oldItem->url(), m_currentItem->url())))
     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());
   m_currentItem->setScrollRestorationType(oldItem->scrollRestorationType());
 
   // The item sequence number determines whether items are "the same", such
   // back/forward navigation between items with the same item sequence number is
   // a no-op. Only treat this as identical if the navigation did not create a
   // back/forward entry and the url is identical or it was loaded via
   // history.replaceState().
@@ skipping 973 matching lines @@
 
 void FrameLoader::restoreScrollPositionAndViewStateForLoadType(
     FrameLoadType loadType) {
   FrameView* view = m_frame->view();
   if (!view || !view->layoutViewportScrollableArea() || !m_currentItem ||
       !m_stateMachine.committedFirstRealDocumentLoad()) {
     return;
   }
   if (!needsHistoryItemRestore(loadType))
     return;
+  if (!m_currentItem->didSaveScrollState())
+    return;
 
   bool shouldRestoreScroll =
       m_currentItem->scrollRestorationType() != ScrollRestorationManual;
   bool shouldRestoreScale = m_currentItem->pageScaleFactor();
 
   // This tries to balance:
   // 1. restoring as soon as possible
   // 2. not overriding user scroll (TODO(majidvp): also respect user scale)
   // 3. detecting clamping to avoid repeatedly popping the scroll position down
   //    as the page height increases
@@ skipping 583 matching lines @@
       frameLoadRequest.clientRedirect());
 
   loader->setLoadType(loadType);
   loader->setNavigationType(navigationType);
   loader->setReplacesCurrentHistoryItem(loadType ==
                                         FrameLoadTypeReplaceCurrentItem);
   return loader;
 }
 
 }  // namespace blink