Reland "Clean up Test's resourcePath code."

This relands commit 91359bed48bc006a4319da86eb26db3b2e6d4afb (Clean up
Test's resourcePath code."

BUG=None
TEST=make dm && out/Debug/dm
R=mtklein@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/321723002
11 files changed