GitLab

Used to take two text files in obscure ninja format, now
expects the targets to compare. e.g.

tools/gn/bin/gyp_flag_compare.py base

or

tools/gn/bin/gyp_flag_compare.py breakpad_processor_support processor_support

TBR=brettw@chromium.org
BUG=335824

Review URL: https://codereview.chromium.org/559853002

Cr-Commit-Position: refs/heads/master@{#294111}