Fix flaky PerfSessionTest due to async access to SharedPrefs

[raymondlam]

shouldCollectGaugesAndEvents_perfMonDisabledAtRuntime_sessionNotVerbose occasionally fails when it tries to programmatically set the config. This is likely due to the ConfigResolver trying to setValue before the shared preferences is ready.

This just forces the test to use a single threaded FakeDirectExecutorService for the DeviceCacheManager

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (ea9775b) and merge commit (5692961).

Test Logs

• Base (ea9775b): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-check-coverage/1490717015915106304
• Merge (5692961): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/3418/check-coverage-changed/1490830947078115328

Notes

• Commit (5692961) is created by Prow via merging PR base commit (ea9775b) and head commit (5ec8fb1).
• Run gradle <product>:checkCoverage to produce HTML coverage reports locally. After gradle commands finished, report files can be found under <product-build-dir>/reports/jacoco/.

1. https://storage.googleapis.com/firebase-sdk-metric-reports/rKB2adPxkx.html

[google-oss-bot]

Size Report ¹

Affected Products

No changes between base commit (ea9775b) and merge commit (5692961).

Test Logs

• Base (ea9775b): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-binary-size/1490717015902523395
• Merge (5692961): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/3418/binary-size/1490830947086503937

Notes

• Commit (5692961) is created by Prow via merging PR base commit (ea9775b) and head commit (5ec8fb1).

1. https://storage.googleapis.com/firebase-sdk-metric-reports/SUCPdvzVpS.html