LoggingFilterInterpreter: Add log path property

The CL add a property for log path so that we can configure
where we want to dump the log at runtime.

BUG=chromium:450159
TEST=deploy and run on device

Change-Id: I34f758dc018011a1e98cf906f8afeed7aeb979ed
Reviewed-on: https://chromium-review.googlesource.com/246870
Reviewed-by: Shyh-In Hwang <josephsih@chromium.org>
Commit-Queue: Tai-Hsu Lin <sheckylin@chromium.org>
Trybot-Ready: Tai-Hsu Lin <sheckylin@chromium.org>
Tested-by: Tai-Hsu Lin <sheckylin@chromium.org>
2 files changed