Update third_party/protobuf to protobuf-v3.0.0-beta-3

third_party/protobuf/python/google/protobuf/pyext/extension_dict.h

Index: third_party/protobuf/python/google/protobuf/pyext/extension_dict.h
diff --git a/third_party/protobuf/python/google/protobuf/pyext/extension_dict.h b/third_party/protobuf/python/google/protobuf/pyext/extension_dict.h
index d92cf956bd8c087a87ceb4d87fc3710e72af0b67..2456eda1e61c56aa471d51943059587691e21bc3 100644
--- a/third_party/protobuf/python/google/protobuf/pyext/extension_dict.h
+++ b/third_party/protobuf/python/google/protobuf/pyext/extension_dict.h
@@ -123,6 +123,12 @@ PyObject* ClearExtension(ExtensionDict* self,
 // Returns a new reference.
 PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* name);
 
+// Gets an extension from the dict given the extension field number as
+// opposed to descriptor.
+//
+// Returns a new reference.
+PyObject* _FindExtensionByNumber(ExtensionDict* self, PyObject* number);
+
 }  // namespace extension_dict
 }  // namespace python
 }  // namespace protobuf