Summary:

clang-format: [JS] unit tests for type aliases.

Also adds a test for "foo as bar" casts.

Spec:
https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#3.10

These are already handled correctly.

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: http://reviews.llvm.org/D19206

llvm-svn: 266744