Factor out SameHost() in registry_controlled_domains

net/base/registry_controlled_domains/registry_controlled_domain.h

Index: net/base/registry_controlled_domains/registry_controlled_domain.h
diff --git a/net/base/registry_controlled_domains/registry_controlled_domain.h b/net/base/registry_controlled_domains/registry_controlled_domain.h
index 89aa6d6c18bc351d26a862a8f8fa79ef70aa325f..19514def02535e8f045798bfcf9d361216775ad8 100644
--- a/net/base/registry_controlled_domains/registry_controlled_domain.h
+++ b/net/base/registry_controlled_domains/registry_controlled_domain.h
@@ -195,11 +195,15 @@ NET_EXPORT base::StringPiece GetDomainAndRegistryAsStringPiece(
 NET_EXPORT std::string GetDomainAndRegistry(base::StringPiece host,
                                             PrivateRegistryFilter filter);
 
+// Returns whether the hosts of the GURLs are identical.

[engedy, 2016/10/21 08:43:22]

nit: Maybe we could put this into the anonymous namespace as well, and only move
the declaration to the header once we actually start using it?

When we do that, we should clarify in one more line what identical means in this
context.

+NET_EXPORT bool SameHost(const GURL& gurl1, const GURL& gurl2);
+
 // These convenience functions return true if the two GURLs or Origins both have
 // hosts and one of the following is true:
 // * They each have a known domain and registry, and it is the same for both
 //   URLs.  Note that this means the trailing dot, if any, must match too.
-// * They don't have known domains/registries, but the hosts are identical.
+// * They don't have known domains/registries, but the hosts are identical
+//   (determined by the SameHost function above).
 // Effectively, callers can use this function to check whether the input URLs
 // represent hosts "on the same site".
 NET_EXPORT bool SameDomainOrHost(const GURL& gurl1, const GURL& gurl2,