Add keeps for strict resource shrinking.

[vkryachko]

Fixes: b/221423396

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (eb7bb1e) and merge commit (49e29f6).

Test Logs

• Base (eb7bb1e): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-check-coverage/1516483108629647360
• Merge (49e29f6): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/3663/check-coverage-changed/1516494559029235712

Notes

• Commit (49e29f6) is created by Prow via merging PR base commit (eb7bb1e) and head commit (1fdd578).
• 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/V2R9qaIHZY.html

[google-oss-bot]

Size Report ¹

Affected Products

• firebase-common

  Type	Base (eb7bb1e)	Merge (49e29f6)	Diff
  aar	48.0 kB	48.5 kB	+585 B (+1.2%)
  apk (aggressive)	84.2 kB	84.6 kB	+322 B (+0.4%)
  apk (release)	680 kB	681 kB	+534 B (+0.1%)

Test Logs

• Base (eb7bb1e): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-binary-size/1516483108629647362
• Merge (49e29f6): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/3663/binary-size/1516494559029235713

Notes

• Commit (49e29f6) is created by Prow via merging PR base commit (eb7bb1e) and head commit (1fdd578).

1. https://storage.googleapis.com/firebase-sdk-metric-reports/ZsN4e00kHc.html