Added basic client hints support.

Source/core/fetch/Resource.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, 2008, 2009, 2010, 2011 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 426 matching lines @@
     setResponse(response);
     m_responseTimestamp = currentTime();
     String encoding = response.textEncodingName();
     if (!encoding.isNull())
         setEncoding(encoding);
 
     if (m_loader) {
         ResourceFetcher* fetcher = ResourceFetcher::toResourceFetcher(m_loader->host());
         if (fetcher && fetcher->frame()) {
             LinkLoader::loadLinkFromHeader(response.httpHeaderField("Link"), fetcher->frame()->document());
+            if (RuntimeEnabledFeatures::clientHintsEnabled() && type() == Resource::MainResource) {
+                String acceptCH = response.httpHeaderField("accept-ch").lower();
+                // FIXME: Write an actual parser for this comma delimited header.

[Mike West, 2015/02/25 09:03:14]

Nit: Can you add a bug ID here?

When you add an actual parser, it would be good to add unit tests as well to
make sure we can easily check the various edge-cases (`dprw`, for instance :) ).

+                if (acceptCH.contains("dpr"))
+                    fetcher->frame()->setShouldSendDPRHint();
+                if (acceptCH.contains("rw"))
+                    fetcher->frame()->setShouldSendRWHint();
+            }
         }
     }
 
     if (!m_resourceToRevalidate)
         return;
     if (response.httpStatusCode() == 304)
         revalidationSucceeded(response);
     else
         revalidationFailed();
 }
@@ skipping 616 matching lines @@
         return "ImportResource";
     case Resource::Media:
         return "Media";
     }
     ASSERT_NOT_REACHED();
     return "Unknown";
 }
 #endif // !LOG_DISABLED
 
 }