Revert "Tree-shaker: Use insertion in the work queue instead of "was compiled" as the criterion to retain a function."
Revert "Tree-shaker: Use insertion in the work queue instead of "was compiled" as the criterion to retain a function."

This reverts commit 908309fe6d239f80711ca4329367974c0265e52f.

Review URL: https://codereview.chromium.org/2199263004 .

dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk