Only attempt to clear measures if we created the measure (#9451)

This fixes an issue where if we decided not to create a measurement we would clear ALL measurements from the performance entry buffer due to passing `undefined` as the entry name.

Author: chrisui

src/renderers/shared/ReactDebugTool.js

@@ -291,7 +291,9 @@ function markEnd(debugID, markType) {
   }
 
   performance.clearMarks(markName);
-  performance.clearMeasures(measurementName);
+  if (measurementName) {
+    performance.clearMeasures(measurementName);
+  }
 }
 
 var ReactDebugTool = {