Fireperf: create a random delay before initiating a remote config fetch.

[leotianlizhan]

Rationale:
This is required to ensure that a remote notification does not trigger multiple config fetches from remote config at the same time. Internal bug reference: b/187985523

iOS version of the same change firebase/firebase-ios-sdk#8593

[google-oss-bot]

Coverage Report

Affected SDKs

• firebase-perf

  SDK overall coverage changed from 70.74% (b9f0ab6) to 70.79% (44dc407b) by +0.05%.

  Filename	Base (b9f0ab6)	Head (44dc407b)	Diff
  RemoteConfigManager.java	92.24%	92.86%	+0.62%

Test Logs

• Base (b9f0ab67): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-check-coverage/1437781317012951044
• Head (44dc407b): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/2968/check-coverage-changed/1438160873125318656

Notes

HTML coverage reports can be produced locally with ./gradlew <product>:checkCoverage.
Report files are located at <product-build-dir>/reports/jacoco/.

Head commit (44dc407b) is created by Prow via merging commits: b9f0ab6 b255861.

[google-oss-bot]

Binary Size Report

Affected SDKs

• firebase-perf

  Type	Base (b9f0ab6)	Head (44dc407b)	Diff
  aar	299 kB	300 kB	+463 B (+0.2%)
  apk (aggressive)	979 kB	980 kB	+284 B (+0.0%)
  apk (release)	2.45 MB	2.45 MB	+408 B (+0.0%)

Test Logs

• Base (b9f0ab67): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-binary-size/1437781317017145345
• Head (44dc407b): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/2968/binary-size/1438160873121124358

Notes

Head commit (44dc407b) is created by Prow via merging commits: b9f0ab6 b255861.

[leotianlizhan]

/retest

[visumickey]

Thanks for making this change @leotianlizhan. Glad to see the changes. I have few comments. PTAL as it permits.

[leotianlizhan]

/retest

[visumickey]

This is great! Thanks for making the changes Leo.

How are you planning to test this? It is important to do some manual testing to make sure we are able fetch the configs in less than 30 seconds and greater than 5 seconds. If you are able to ascertain that, please feel free to merge this change.

[leotianlizhan]

This is great! Thanks for making the changes Leo.

How are you planning to test this? It is important to do some manual testing to make sure we are able fetch the configs in less than 30 seconds and greater than 5 seconds. If you are able to ascertain that, please feel free to merge this change.

yes I've done some manual testing and it looks like it works