Add support for mojom and typemap files in tools/boilerplate.py

Bug: None
Change-Id: I0d56179e339c4c361823f438b7d70072de80ee59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1602712Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Tanmoy Mollik <triploblastic@google.com>
Cr-Commit-Position: refs/heads/master@{#658494}

tools/boilerplate.py

@@ -28,6 +28,8 @@ EXTENSIONS_TO_COMMENTS = {
     'py': '#',
     'gn': '#',
     'gni': '#',
+    'mojom': '//',
+    'typemap': '#',
 }
 
 def _GetHeader(filename):