Add a Dns preresolve interface in //content

chrome/browser/chromeos/login/auth/auth_prewarmer.cc

Index: chrome/browser/chromeos/login/auth/auth_prewarmer.cc
diff --git a/chrome/browser/chromeos/login/auth/auth_prewarmer.cc b/chrome/browser/chromeos/login/auth/auth_prewarmer.cc
index 6ebf6bfa231768c524a921ac57b8ec7ab1bde069..ecea1d1c0666606b17e185b92f56ec38a55d9d2e 100644
--- a/chrome/browser/chromeos/login/auth/auth_prewarmer.cc
+++ b/chrome/browser/chromeos/login/auth/auth_prewarmer.cc
@@ -96,9 +96,8 @@ void AuthPrewarmer::DoPrewarm() {
   const GURL& url = GaiaUrls::GetInstance()->service_login_url();
   content::BrowserThread::PostTask(
       content::BrowserThread::IO, FROM_HERE,
-      base::Bind(&content::PreconnectUrl,
-                 base::RetainedRef(GetRequestContext()), url, url,
-                 kConnectionsNeeded, true,
+      base::Bind(&content::PreconnectUrl, login::GetSigninResourceContext(),

[achuithb, 2016/05/25 21:17:10]

Why not
ProfileHelper::GetSigninProfile()->GetResourceContext() here?

[Charlie Harrison, 2016/05/25 21:36:19]

That's much better. Done.

+                 url, url, kConnectionsNeeded, true,
                  net::HttpRequestInfo::EARLY_LOAD_MOTIVATED));
   if (!completion_callback_.is_null()) {
     content::BrowserThread::PostTask(content::BrowserThread::UI, FROM_HERE,