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This fixes a number of small issues I found while actually testing
things to get it ready to run on the bots. In particular, 'mb analyze'
didn't work right for GN. Tests were added.

TBR=brettw@chromium.org
BUG=466436

Review URL: https://codereview.chromium.org/1074583002

Cr-Commit-Position: refs/heads/master@{#324312}