static browserSupportsUncompiledMode() {
    // Check if ES6 arrow function syntax and ES7 async are usable.  Both are
    // needed for uncompiled builds to work.
    try {
      eval('async ()=>{}');
      return true;
    } catch (e) {
      return false;
    }
  }
@return {boolean} True if the browser would support the uncompiled build.