Make PageScaleFactor work for oopif subframes.

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 1424 matching lines @@
     // is an old version of HistoryItem so distribute the scroll between
     // the main frame and the visual viewport as best as we can.
     if (visualViewportOffset.width() == -1 &&
         visualViewportOffset.height() == -1) {
       visualViewportOffset =
           m_currentItem->getScrollOffset() -
           view->layoutViewportScrollableArea()->getScrollOffset();
     }
 
     VisualViewport& visualViewport = m_frame->host()->visualViewport();
+    float originalScale = visualViewport.scale();
     if (shouldRestoreScale && shouldRestoreScroll) {
       visualViewport.setScaleAndLocation(m_currentItem->pageScaleFactor(),
                                          FloatPoint(visualViewportOffset));
     } else if (shouldRestoreScale) {
       visualViewport.setScale(m_currentItem->pageScaleFactor());
     } else if (shouldRestoreScroll) {
       visualViewport.setLocation(FloatPoint(visualViewportOffset));
     }
+    // If necessary, notify client we've restored page scale.
+    if (shouldRestoreScale && (originalScale != visualViewport.scale()))
+      client()->didRestorePageScaleFactorOnLoad(visualViewport.scale());

[kenrb, 2017/01/24 17:13:27]

I am not clear on why this is necessary. Does this code path imply that we have
just completed a page load? Doesn't that mean that previously-existing OOPIFs
will all have been destroyed?

[wjmaclean, 2017/01/24 18:24:26]

Hmm, I don't think so, otherwise one would not expect this to work on pages with
oopif subframes, and it seems to. Wouldn't it make sense that any previously
destroyed subframes would be re-created by the time the page load is completed?

I think any subframes that load later get the PSF from the WebContents as they
are loaded, but I'll have to verify that.

[kenrb, 2017/01/24 18:47:30]

What I meant was, if the frames have been destroyed and recreated, wouldn't they
have had their page scale factors reset anyway, because each would have a newly
initialized compositor?

 
     if (ScrollingCoordinator* scrollingCoordinator =
             m_frame->page()->scrollingCoordinator())
       scrollingCoordinator->frameViewRootLayerDidChange(view);
   }
 
   documentLoader()->initialScrollState().didRestoreFromHistory = true;
 }
 
 String FrameLoader::userAgent() const {
@@ skipping 464 matching lines @@
                          m_documentLoader ? m_documentLoader->url() : String());
   return tracedValue;
 }
 
 inline void FrameLoader::takeObjectSnapshot() const {
   TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID("loading", "FrameLoader", this,
                                       toTracedValue());
 }
 
 }  // namespace blink