Roll engine c3b63d610b07..49971e21402e (3 commits) (#43673)

git@github.com:flutter/engine.git/compare/c3b63d610b07...49971e21402e

git log c3b63d610b07..49971e21402e --no-merges --oneline
2019-10-28 yjbanov@google.com Implement basic Picture.toImage via BitmapCanvas (flutter/engine#13391)
2019-10-28 chinmaygarde@google.com Switch the MacOS Desktop embedder to using a thread configuration where the platform and render task runners are the same. (flutter/engine#13300)
2019-10-28 skia-flutter-autoroll@skia.org Roll src/third_party/skia 18f5b1a6dd77..1beb8ae9a2f5 (9 commits) (flutter/engine#13392)


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 aaclarke@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