Fix loading placeholders for Lo-Fi

third_party/WebKit/Source/core/fetch/ImageResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 499 matching lines @@
 }
 
 void ImageResource::reloadIfLoFi(ResourceFetcher* fetcher)
 {
     if (!m_response.httpHeaderField("chrome-proxy").contains("q=low"))
         return;
     m_resourceRequest.setCachePolicy(WebCachePolicy::BypassingCache);
     m_resourceRequest.setLoFiState(WebURLRequest::LoFiOff);
     if (isLoading())
         m_loader->cancel();
-    else
-        updateImageAndClearBuffer();
+    error(ResourceError::cancelledError(url()));

[hiroshige, 2016/07/04 12:02:29]

Instead of calling error(), how about
    clear();
    m_data.clear();
(i.e. not calling |updateImage(true)|), or
    clear();
    m_data.clear();
    notifyObservers();
(See Patch Set 1 of https://chromiumcodereview.appspot.com/1928823002/#ps1)?

IIUC, the image is not update because, in updateImageAndClearBuffer(),
updateImage(true) is called after clearImage(), and here |m_image| is non-null
and points to the old image, and |m_image| is not re-created or updated after
reloadIfLoFi().
If so, not calling |updateImage(true)| might resolve the problem.

I'd like to avoid using error() here, because calling error() after finish()
looks strange, and doing what is needed for reloading explicitly here would be
clearer than depending on error() (that does many things).

[megjablon, 2016/07/07 00:51:57]

Thanks! Was looking for another way that would load the images properly, but was
confused why updateImageAndClearBuffer didn't work.

     setStatus(NotStarted);
     fetcher->startLoad(this);
 }
 
 void ImageResource::changedInRect(const blink::Image* image, const IntRect& rect)
 {
     if (!image || image != m_image)
         return;
     notifyObservers(&rect);
 }
@@ skipping 32 matching lines @@
     if (response().wasFetchedViaServiceWorker())
         return response().serviceWorkerResponseType() != WebServiceWorkerResponseTypeOpaque;
     if (!getImage()->currentFrameHasSingleSecurityOrigin())
         return false;
     if (passesAccessControlCheck(securityOrigin))
         return true;
     return !securityOrigin->taintsCanvas(response().url());
 }
 
 } // namespace blink