Setup test infra into mapBuffer project

Summary:
Setup test infra into mapBuffer project

changelog: [internal]

Reviewed By: JoshuaGross

Differential Revision: D25733949

fbshipit-source-id: bcfc89d87e28dc5a6ed28bc6b56893aa6f191e71

ReactCommon/react/renderer/mapbuffer/MapBuffer.cpp

@@ -14,5 +14,9 @@ MapBuffer::MapBuffer() {}
 
 MapBuffer::~MapBuffer() {}
 
+int MapBuffer::getSize() {
+  return 0;
+}
+
 } // namespace react
 } // namespace facebook