The third attempt never landed :). This attempt completely reworks
the logic to attempt to be clearer and more obviously correct. This
attempt also actually had unit tests written for it (see bug 625353).

R=machenbach@chromium.org
BUG=625353, 629825
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_compile_x86_dbg,android_compile_mips_dbg,android_arm64_dbg_recipe

Review-Url: https://codereview.chromium.org/2173343002
Cr-Commit-Position: refs/heads/master@{#37999}