Make net_unittests_run work with component=shared_library.

Specifically, this adds support to run net_unittests isolated via 'isolate.py
run' when built with component build.

R=vadimsh@chromium.org,brettw@chromium.org,rsleevi@chromium.org
BUG=336439

Review URL: https://codereview.chromium.org/134003004

git-svn-id: https://src.chromium.org/chrome/trunk/src/url@249150 4ff67af0-8c30-449e-8e8b-ad334ec8d88c