GN: Allow escape codes to be embedded in strings via $0xFF

I've wanted to use them when writing assert messages. Might also be
useful in write_file().

BUG=

Review URL: https://codereview.chromium.org/1546393002

Cr-Original-Commit-Position: refs/heads/master@{#367622}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f59e82f6169caace177e452c06377b3d611ed978
3 files changed
tree: d3d6354b00fe7809af693334c860d0e46ed05d31
  1. tools/