Support Promise<T> syntax in the IDL parser.

The Web IDL spec specifies Promise<T> syntax. This CL makes the IDL parser
recognize the syntax.

BUG=421539

Review URL: https://codereview.chromium.org/653343002

Cr-Original-Commit-Position: refs/heads/master@{#300255}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6ce2b8e162baa9573aaa1819ac610ef854cca9f8
6 files changed