Fix a bug in `gn analyze` related to build-only changes.

`gn analyze` would incorrectly claim that no compile was necessary
if given a list of files that included build file changes but not
any source file changes.

R=brettw@chromium.org
BUG=648448

Review-Url: https://codereview.chromium.org/2355713002
Cr-Original-Commit-Position: refs/heads/master@{#419662}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 253b1190a67b4ccac5c8b2583e6b19c6a1c5e3f9
2 files changed
tree: 1a65e33c5334d95978734da23a814760bf867b11
  1. tools/