[Closure Compile GN] Update Closure docs.

This CL updates Chromium Closure Compilation docs to use GN-based
compilation.

Bug: 632206
Change-Id: Ie3aef4b7f81744e04051489731acf4e7aa80da15
Reviewed-on: https://chromium-review.googlesource.com/1098749
Reviewed-by: Demetrios Papadopoulos <[email protected]>
Commit-Queue: calamity <[email protected]>
Cr-Commit-Position: refs/heads/master@{#567116}
2 files changed