Fix some typos in GN documentation.

Review URL: https://codereview.chromium.org/1338003005

Cr-Original-Commit-Position: refs/heads/master@{#348497}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 91e3ca5ba9866da089ef6b37fdba3d84f7e51602
3 files changed
tree: 2abbb7153eeeb17394629b15725c216efcbfbe58
  1. tools/