Roll engine ab097a59faf5..1efb5b770c97 (2 commits) (#39004)

git@github.com:flutter/engine.git/compare/ab097a59faf5...1efb5b770c97

git log ab097a59faf5..1efb5b770c97 --no-merges --oneline
2019-08-21 dnfield@google.com update sim script (flutter/engine#11355)
2019-08-21 dnfield@google.com Firebase test for Platform Views on iOS (flutter/engine#11350)

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bin/internal/engine.version

-ab097a59faf50fd0335d26709b88955b2b2dcc06
+1efb5b770c97160f91fc8cfa5cc7f54954b64d60