Turn off ipv6 when there is no support at startup.

IPv6 confusion (attempt to support when it is really
not supported) has been harming performance, and this
may help *some* users that don't have ipv6 support.

BUG=12754
r=wtc
Review URL: http://codereview.chromium.org/564052

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@38078 0039d316-1c4b-4281-b951-d872f2087c98

net/base/host_resolver_impl.cc

@@ -53,6 +53,8 @@ HostResolver* CreateSystemHostResolver(
   HostResolverImpl* resolver = new HostResolverImpl(
       NULL, CreateDefaultCache(), network_change_notifier, kMaxJobs);
 
+  if (!HostResolverProc::IPv6Supported())
+    resolver->SetDefaultAddressFamily(net::ADDRESS_FAMILY_IPV4);
   return resolver;
 }
 

net/base/host_resolver_proc.cc

@@ -227,4 +227,27 @@ int SystemHostResolverProc(const std::string& host,
   return OK;
 }
 
+// TODO(jar): The following is a simple estimate of ipv6 support.  We may need
+// to do a test resolution, and a test connection, to REALLY verify support.
+// static
+bool HostResolverProc::IPv6Supported() {
+#if defined(OS_POSIX)
+  int test_socket;
+#else
+  SOCKET test_socket;
+#endif
+
+  test_socket = socket(AF_INET6, SOCK_STREAM, 0);
+  if (test_socket == -1)
+    return false;
+
+#if defined(OS_POSIX)
+  close(test_socket);
+#else
+  closesocket(test_socket);
+#endif
+
+  return true;
+}
+
 }  // namespace net

net/base/host_resolver_proc.h

@@ -32,6 +32,9 @@ class HostResolverProc : public base::RefCountedThreadSafe<HostResolverProc> {
                       AddressFamily address_family,
                       AddressList* addrlist) = 0;
 
+  // Test to see if IPv6 is supported.
+  static bool IPv6Supported();
+
  protected:
   friend class base::RefCountedThreadSafe<HostResolverProc>;