Roll engine 7a77e3625dd1..a38839817cda (4 commits) (#45355)

git@github.com:flutter/engine.git/compare/7a77e3625dd1...a38839817cda

git log 7a77e3625dd1..a38839817cda --no-merges --oneline
2019-11-21 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/linux-amd64 from VHWsK... to zgJ75... (flutter/engine#13957)
2019-11-21 bkonyi@google.com Roll src/third_party/dart 867a6e0e52..aa2b3a5eaa (15 commits) (flutter/engine#13955)
2019-11-21 30870216+gaaclarke@users.noreply.github.com Made the thread checker print out the thread names on Apple platforms. (flutter/engine#13943)
2019-11-21 liyuqian@google.com Fix picture raster cache throttling (flutter/engine#13710)


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

bin/internal/engine.version

-7a77e3625dd1db5f4f517a129707cb299c48207a
+a38839817cda09745ac64517b155e097e00dc786