Executed HTTPS upgrade before notifying the start of the provisional load.

third_party/WebKit/Source/core/fetch/ResourceFetcher.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) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
     Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
 
     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 392 matching lines @@
     // |m_preloads| only, because they are major sources of references.
     if (resource && !resource->hasClientsOrObservers() && (!m_preloads || !m_preloads->contains(resource))) {
         DEFINE_RESOURCE_HISTOGRAM("Dead.");
     }
 }
 
 Resource* ResourceFetcher::requestResource(FetchRequest& request, const ResourceFactory& factory, const SubstituteData& substituteData)
 {
     ASSERT(request.options().synchronousPolicy == RequestAsynchronously || factory.type() == Resource::Raw || factory.type() == Resource::XSLStyleSheet);
 
-    context().upgradeInsecureRequest(request);
+    if (request.resourceRequest().httpHeaderField("Upgrade-Insecure-Requests") != AtomicString("1"))

[Mike West, 2016/07/04 08:33:25]

1. Can you add a comment describing the rationale for checking the header's
presence?

2. This could probably be moved into `FrameFetchContext::upgradeInsecureRequest`
as an early-exit, rather than complicating the callsites.

[carlosk, 2016/07/04 09:22:59]

Both done. Much better indeed.

+        context().upgradeInsecureRequest(request.mutableResourceRequest());
     context().addClientHintsIfNecessary(request);
     context().addCSPHeaderIfNecessary(factory.type(), request);
 
     TRACE_EVENT1("blink", "ResourceFetcher::requestResource", "url", urlForTraceEvent(request.url()));
 
     if (!request.url().isValid())
         return nullptr;
 
     if (!context().canRequest(factory.type(), request.resourceRequest(), MemoryCache::removeFragmentIdentifierIfNeeded(request.url()), request.options(), request.forPreload(), request.getOriginRestriction()))
         return nullptr;
@@ skipping 837 matching lines @@
     visitor->trace(m_context);
     visitor->trace(m_archive);
     visitor->trace(m_loaders);
     visitor->trace(m_nonBlockingLoaders);
     visitor->trace(m_documentResources);
     visitor->trace(m_preloads);
     visitor->trace(m_resourceTimingInfoMap);
 }
 
 } // namespace blink