This didn't break anything that we know of, but the engine is not
currently rollable to the framework due to a Dart bug. I'm reverting
this so we can get a fix landed for the Dart SDK, then roll, then
re-land this, then roll, to allow us to measure the performance impact
of the Dart SDK roll and the Skia roll independently.
This reverts commit 55b5f7dca6.