Add support for module-definition files to gn

BUG=

Review URL: https://codereview.chromium.org/1160773002

Cr-Original-Commit-Position: refs/heads/master@{#332355}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: b73b2de6a23e3220c79c6bb9e9f3a7b4dd20d2dd
6 files changed
tree: 3e0227df6051e32c50e64f484a77ad8623af3bee
  1. tools/