Fix metrics_unittests on Android.

The metrics_unittests tried to write an empty file to the
current working directory, which caused a crash on Android. By
using the output folder instead, this is avoided.
This makes it possible to re-enable the tests disabled in r4474
and also remove the empty dummy test added in r4627.

BUG=1882,
TEST=Setup a Chromium+WebRTC checkout as described in issue 1882
. build/android/envsetup.sh
export GYP_DEFINES="$GYP_DEFINES include_tests=1 enable_tracing=1"
gclient runhooks
ninja -C out/Release metrics_unittests_apk
build/android/test_runner.py gtest -s metrics_unittests --verbose --release

R=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2127006

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4634 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed