Run shell tests on android.

This CL enables shell tests on android.

For this, it embeds test applications in the test apk, and copied those
on disk as needed. It also refactor FileHelper so that it keeps a
timestamp of the last apk it was used with to allow no to re-extract
files that are already up to date.

R=ppi@chromium.org, viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/815993004