Roll engine cef6751dba87..e78c3f59c1a1 (2 commits) (#42495)

git@github.com:flutter/engine.git/compare/cef6751dba87...e78c3f59c1a1

git log cef6751dba87..e78c3f59c1a1 --no-merges --oneline
2019-10-11 iska.kaushik@gmail.com [dart_aot_runner] Add support for generating dart_aot snapshots (flutter/engine#13071)
2019-10-10 chinmaygarde@gmail.com Put Metal renderer selection behind runtime flag and plist opt-in. (flutter/engine#13056)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC chinmaygarde@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

bin/internal/engine.version

-cef6751dba87e144ced30501b205450546506177
+e78c3f59c1a105e216e00db105d4f7391ccf01c1