clang-format: [JS] Support TypeScript 1.6 user defined type guards.

Before:
  function foo(check: Object): check
  is{foo: string, bar: string, baz: string, foobar: string} {
    return 'bar' in check;
  }

After:
  function foo(check: Object):
      check is {foo: string, bar: string, baz: string, foobar: string} {
    return 'bar' in check;
  }

llvm-svn: 256631