Avoid unnecessary std::string allocations.

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 24ffb707a50ab5fd44e7b7f86427a9dfd0bff8b6..1c2f56dfa2aaee1084b1715cacc5cfc26038b935 100644
--- a/net/base/registry_controlled_domains/registry_controlled_domain.h
+++ b/net/base/registry_controlled_domains/registry_controlled_domain.h
@@ -182,6 +182,13 @@ enum UnknownRegistryFilter {
 NET_EXPORT std::string GetDomainAndRegistry(const GURL& gurl,
                                             PrivateRegistryFilter filter);
 
+// Same as above, but returns a part of |gurl|'s host in a StringPiece.

[engedy, 2016/09/28 17:22:52]

Phrasing nit: ... returns the domain and registry as a StringPiece that
references the underlying string of the passed-in |gurl|.

[pkalinnikov, 2016/10/05 11:51:35]

Done.

+// TODO(pkalinnikov): Rename this to GetDomainAndRegistry and get rid of the

[engedy, 2016/09/28 17:22:52]

As discussed, please run some quick tests to see how often this is called during
normal browsing, e.g. by adding TRACE_EVENT inside.

If called often, I agree that we should file a bug documenting that fact,
reference that bug here in this CL, then update all existing call sites in a
follow-up CL and remove this TODO.

[pkalinnikov, 2016/10/05 11:51:35]

It is used not frequently during normal browsing. In a small experiment I
collected 9 calls, which was roughly the number of times I clicked some
hyperlink.

Can I leave the TODO?

[engedy, 2016/10/05 11:58:14]

Usually it's recommended to leave a TODO only if we are actually planning to do
this refactor in the near future, and in that case we should file a bug to track
it.

I'd leave it up to Peter to decide if the refactor is worth it in light of how
rarely this is called.

+// std::string-returning version. Update clients.
+NET_EXPORT base::StringPiece GetDomainAndRegistryAsStringPiece(
+    const GURL& gurl,
+    PrivateRegistryFilter filter);
+
 // Like the GURL version, but takes a host (which is canonicalized internally)
 // instead of a full GURL.
 NET_EXPORT std::string GetDomainAndRegistry(base::StringPiece host,