[Extern Generation] Add a presubmit script to check externs not being updated
Add a presubmit script that checks for when extension api files are touched, but
the corresponding extern file is not. Right now, this is very simple - it only
checks that the extern is modified in some way (doesn't validate that it's the
*right* way), and is only a warning (because sometimes api file changes don't
cause extern changes). As an improvement, we would validate that the extern
files contain the proper content - let's do that later.
This will also be rolled out piecemeal, since many APIs don't currently have a
dedicated extern file. This change only imposes the check on bluetooth (because
it was handy) - if all goes well, we'll roll this out to all api files.
Also establish a dedicated extern folder, since it's silly for chrome-generated
externs to live in third_party/.
BUG=469920
Review URL: https://codereview.chromium.org/1718243003
Cr-Commit-Position: refs/heads/master@{#378018}
4 files changed
