Actually handle the Vary header in blink, rather than punting on sight.

third_party/WebKit/Source/platform/loader/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
@@ skipping 965 matching lines @@
       return false;
   }
   return true;
 }
 
 bool Resource::hasCacheControlNoStoreHeader() const {
   return response().cacheControlContainsNoStore() ||
          resourceRequest().cacheControlContainsNoStore();
 }
 
-bool Resource::hasVaryHeader() const {
-  return !response().httpHeaderField(HTTPNames::Vary).isNull();
+bool Resource::mustReloadDueToVaryHeader(
+    const ResourceRequest& newRequest) const {
+  const AtomicString& vary = response().httpHeaderField(HTTPNames::Vary);
+  if (vary.isNull())
+    return false;
+  if (vary == "*")
+    return true;
+
+  CommaDelimitedHeaderSet varyHeaders;
+  parseCommaDelimitedHeader(vary, varyHeaders);
+  for (const String& header : varyHeaders) {
+    AtomicString atomicHeader(header);
+    if (resourceRequest().httpHeaderField(atomicHeader) !=
+        newRequest.httpHeaderField(atomicHeader)) {
+      return true;
+    }
+  }
+  return false;
 }
 
 bool Resource::mustRevalidateDueToCacheHeaders() const {
   return !canUseResponse(response(), m_responseTimestamp) ||
          resourceRequest().cacheControlContainsNoCache() ||
          resourceRequest().cacheControlContainsNoStore();
 }
 
 bool Resource::canUseCacheValidator() const {
   if (isLoading() || errorOccurred())
@@ skipping 111 matching lines @@
     case Resource::Media:
     case Resource::Manifest:
     case Resource::Mock:
       return false;
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace blink