Added basic client hints support.

Source/core/fetch/Resource.cpp

Index: Source/core/fetch/Resource.cpp
diff --git a/Source/core/fetch/Resource.cpp b/Source/core/fetch/Resource.cpp
index 63f7bf6dc8785eadfd0a034e928c96748e26e681..753cea2524f08e80efa3af4744640ab2ef6af531 100644
--- a/Source/core/fetch/Resource.cpp
+++ b/Source/core/fetch/Resource.cpp
@@ -444,6 +444,14 @@ void Resource::responseReceived(const ResourceResponse& response, PassOwnPtr<Web
         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();
+            }
         }
     }