Add a new GetNegotiatedProtocol method to StreamSocket and implement in all subclasses.

net/socket/client_socket_pool_base_unittest.cc

Index: net/socket/client_socket_pool_base_unittest.cc
diff --git a/net/socket/client_socket_pool_base_unittest.cc b/net/socket/client_socket_pool_base_unittest.cc
index b1c1a99e1ed7edbd3fb8bfb724b776e6d173aa5f..20cf1d3ad3ba31173259cf096a5726dac7bcecc0 100644
--- a/net/socket/client_socket_pool_base_unittest.cc
+++ b/net/socket/client_socket_pool_base_unittest.cc
@@ -103,6 +103,9 @@ class MockClientSocket : public StreamSocket {
         base::TimeDelta::FromMicroseconds(10);
     return kDummyConnectTimeMicros;  // Dummy value.
   }
+  virtual NextProto GetNegotiatedProtocol() const {
+    return kProtoUnknown;
+  }
 
  private:
   bool connected_;