Combine displayName using underscore

Author: subtleGradient

src/test/ReactPerf.js

@@ -56,7 +56,7 @@ var ReactPerf = {
  }
  return func.apply(this, arguments);
  };
- wrapper.displayName = objName + '.' + fnName;
+ wrapper.displayName = objName + '_' + fnName;
  return wrapper;
  }
  return func;