GitLab

  In order to roll GN c99acd65..5c18ca83 (r439377:r442253) and pick up
  the following changes:

  4ce240b3 Associate xctest files with corresponding xctest targets.
  7e5894a9 Configure xctest build settings to prevent Xcode from linking objects.
  043a15dd Add functionality to find xctest files under application target.
  d1316080 Stop propagation of dependent configs between toolchains.
  0c1dd9de GN: Fix some typos in the documentation.
  67e8c60e [Refactor Xcode Objects] Allow extra attributes for native targets.
  8fb7d9d9 [Refactor Xcode Objects] Enable adding per file '--help' compiler flag.
  898a56b7 [Refactor Xcode Objects] Decouple file references and indexing target.
  a8936b7a Fix a typo in GN documentation
  889ccd0f Fix a typo in gn help.
  7d886382 Support for source_target_relative expansion in GN
  615f8527 Fix GN bootstrap.
  d48f4812 [Refactor Xcode Objects] Enable navigator paths for file references.
  44dbd2f1 Clean up link references in //tools/gn/README.md.

TBR=dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2619823002
Cr-Commit-Position: refs/heads/master@{#442988}