Add an output_dir override to GN.

This adds support for the ability for targets to override their output
directory. The tool defines a default output directory in terms of the normal
patterns. The target can optionally supply an override, and the tool uses the
new {{output_dir}} pattern when specifying tool output to express the result of
the default-or-override.

Review URL: https://codereview.chromium.org/1887533003

Cr-Original-Commit-Position: refs/heads/master@{#387366}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f2eba7f76b6effb82ddce70d2bb227f4e25b1f69
16 files changed
tree: 4baea421044b6ed13582d84c2149c5c8beb59672
  1. tools/