Make PRESUBMIT.py validate WATCHLISTS by scanning an AST tree

Bug: 
Change-Id: I51ac893e8470f28a22ccfc949e8ca2cb0f368d02
Reviewed-on: https://chromium-review.googlesource.com/598761
Commit-Queue: Takeshi Yoshino <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#493357}
1 file changed