Add a Dns preresolve interface in //content

content/public/browser/resource_hints.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_RESOURCE_HINTS_H_
 #define CONTENT_PUBLIC_BROWSER_RESOURCE_HINTS_H_
 
 #include "content/common/content_export.h"
+#include "net/base/completion_callback.h"
 #include "net/http/http_request_info.h"
 #include "url/gurl.h"
 
 class GURL;
 
 namespace net {
 class URLRequestContextGetter;
 }
 
 namespace content {
 
+// TODO(csharrison): A cleaner interface woulbe to use ResourceContext instead
+// of URLRequestContextGetter for these functions. The predictor will need to be
+// modified for this purpose to guarantee lifetime semantics.
+
 // A Preconnect instance maintains state while a TCP/IP connection is made, and
 // then released into the pool of available connections for future use.
 
 // Tries to preconnect. |count| may be used to request more than one connection
 // be established in parallel. Note that the net stack has logic so multiple
 // calls to preconnect a given url within a short time frame will automatically
 // coalesce. |allow_credentials| corresponds to the fetch spec.
 // Note: This should only be called on the IO thread, with a valid
 // URLRequestContextGetter.
 CONTENT_EXPORT void PreconnectUrl(
     net::URLRequestContextGetter* getter,
     const GURL& url,
     const GURL& first_party_for_cookies,
     int count,
     bool allow_credentials,
     net::HttpRequestInfo::RequestMotivation motivation);
 
+// Issues a DNS request to |url|. Note that these requests are sent to the host
+// resolver with priority net::IDLE.
+CONTENT_EXPORT int PreresolveUrl(net::URLRequestContextGetter* getter,
+                                 const GURL& url,
+                                 const net::CompletionCallback& callback);
+
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RESOURCE_HINTS_H_