Fix GN bootstrap.

Update list of required files and compile flags.

BUG=None

Review-Url: https://codereview.chromium.org/2588003002
Cr-Original-Commit-Position: refs/heads/master@{#439509}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 615f852746f6a8c1331eec32e8352d7cfcd63f76