code: function getUniqueIdentifierName(scopes, prefix, num) {
          if (!scopes) {
              return prefix;
          }
  
          var props = scopes.reduce(function(props, scope) {
              return _.union(props, _.keys(scope.props));
          }, []);
  
          if (!props) {
              return prefix;
          }
  
          num = num || "1";
          var name;
          while (num < 100) { // limit search length
              name = prefix + num;
              if (props.indexOf(name) === -1) {
                  break;
              }
              ++num;
          }
          return name;
      }
docs: Gets a unique identifier name in the scope that starts with prefix
  @param {!Scope} scopes - an array of all scopes returned from tern (each element contains 'props' with identifiers
  in that scope)
  @param {!string} prefix - prefix of the identifier
  @param {number} num - number to start checking for
  @return {!string} identifier name