Avoid unnecessary std::string allocations.

net/base/registry_controlled_domains/registry_controlled_domain.cc

Index: net/base/registry_controlled_domains/registry_controlled_domain.cc
diff --git a/net/base/registry_controlled_domains/registry_controlled_domain.cc b/net/base/registry_controlled_domains/registry_controlled_domain.cc
index 8d379ba91b7f486df8d6593bf76ff13de8b5f885..ca367f7214297509d21ea2f3e0bb8284e2ef855a 100644
--- a/net/base/registry_controlled_domains/registry_controlled_domain.cc
+++ b/net/base/registry_controlled_domains/registry_controlled_domain.cc
@@ -148,22 +148,23 @@ size_t GetRegistryLengthImpl(base::StringPiece host,
       (host.length() - curr_start) : 0;
 }
 
-std::string GetDomainAndRegistryImpl(base::StringPiece host,
-                                     PrivateRegistryFilter private_filter) {
+base::StringPiece GetDomainAndRegistryImpl(
+    base::StringPiece host,
+    PrivateRegistryFilter private_filter) {
   DCHECK(!host.empty());
 
   // Find the length of the registry for this host.
   const size_t registry_length =
       GetRegistryLengthImpl(host, INCLUDE_UNKNOWN_REGISTRIES, private_filter);
   if ((registry_length == std::string::npos) || (registry_length == 0))
-    return std::string();  // No registry.
+    return base::StringPiece();  // No registry.
   // The "2" in this next line is 1 for the dot, plus a 1-char minimum preceding
   // subcomponent length.
   DCHECK(host.length() >= 2);
   if (registry_length > (host.length() - 2)) {
     NOTREACHED() <<
         "Host does not have at least one subcomponent before registry!";
-    return std::string();
+    return base::StringPiece();
   }
 
   // Move past the dot preceding the registry, and search for the next previous
@@ -171,8 +172,8 @@ std::string GetDomainAndRegistryImpl(base::StringPiece host,
   // no dot.
   const size_t dot = host.rfind('.', host.length() - registry_length - 2);
   if (dot == std::string::npos)
-    return host.as_string();
-  return host.substr(dot + 1).as_string();
+    return host;
+  return host.substr(dot + 1);
 }
 
 }  // namespace
@@ -180,9 +181,15 @@ std::string GetDomainAndRegistryImpl(base::StringPiece host,
 std::string GetDomainAndRegistry(
     const GURL& gurl,
     PrivateRegistryFilter filter) {
+  return GetDomainAndRegistryAsStringPiece(gurl, filter).as_string();
+}
+
+base::StringPiece GetDomainAndRegistryAsStringPiece(

[Peter Kasting, 2016/10/06 06:21:35]

For now, I would move this function into the anonymous namespace above and
remove it from the .h, since it's not called outside the class.

I'm not opposed to changing the public interface of the class to use
StringPieces if it makes sense.  (That would probably be better than have string
and StringPiece variants of some of the functions there.)  However, let's not
touch the header until we're actually going to do that.

If you want to pursue it, I suggest filing a bug against yourself about this and
adding a TODO on this helper to eliminate it by exposing StringPiece as the
interface type for all these APIs.  However, StringPiece can be viral, and it
would be sad to add 50 .as_string() calls in the callers if that didn't end up
being a timesave.

[pkalinnikov, 2016/10/06 10:51:36]

Done.

+    const GURL& gurl,
+    PrivateRegistryFilter filter) {
   base::StringPiece host = gurl.host_piece();
   if (host.empty() || gurl.HostIsIPAddress())
-    return std::string();
+    return base::StringPiece();
   return GetDomainAndRegistryImpl(host, filter);
 }
 
@@ -192,7 +199,7 @@ std::string GetDomainAndRegistry(base::StringPiece host,
   const std::string canon_host(CanonicalizeHost(host, &host_info));
   if (canon_host.empty() || host_info.IsIPAddress())
     return std::string();
-  return GetDomainAndRegistryImpl(canon_host, filter);
+  return GetDomainAndRegistryImpl(canon_host, filter).as_string();
 }
 
 bool SameDomainOrHost(
@@ -201,8 +208,10 @@ bool SameDomainOrHost(
     PrivateRegistryFilter filter) {
   // See if both URLs have a known domain + registry, and those values are the
   // same.
-  const std::string domain1(GetDomainAndRegistry(gurl1, filter));
-  const std::string domain2(GetDomainAndRegistry(gurl2, filter));
+  const base::StringPiece domain1 =
+      GetDomainAndRegistryAsStringPiece(gurl1, filter);
+  const base::StringPiece domain2 =
+      GetDomainAndRegistryAsStringPiece(gurl2, filter);
   if (!domain1.empty() || !domain2.empty())
     return domain1 == domain2;