Support using gtest_filter and test-launcher-filter-file together on Android

These args used to be mutually exclusive, which would cause errors when
retrying the Android network service tests (which use
--test-launcher-filter-file). This combines the filters specified in the
filter file with the gtest_filter argument.

See here for an example of a failure:
https://chromium-swarm.appspot.com/task?id=41984d0ac388e010

Bug: 880915
Change-Id: I2fee107d13c44bd90cd9532bcabda4bb12f7e111
Reviewed-on: https://chromium-review.googlesource.com/c/1364071
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614509}
2 files changed