Roll engine 51a79649662f..4218f8026f29 (14 commits) (#49470)

https://github.com/flutter/engine/compare/51a79649662f...4218f8026f29

git log 51a79649662f..4218f8026f29 --first-parent --oneline
2020-01-25 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/mac-amd64 from 7fqYj... to 35pbn... (flutter/engine#15984)
2020-01-25 nurhan@google.com updating the versions of the browsers for flutter web engine unit tests (flutter/engine#15977)
2020-01-25 chris@bracken.jp Eliminate unused import in Android embedding (flutter/engine#15975)
2020-01-24 matthew-carroll@users.noreply.github.com Prevent duplicate plugin registration in FlutterEnginePluginRegistry. (#49365) (flutter/engine#15956)
2020-01-24 dnfield@google.com retry logic for another cipd upload (flutter/engine#15974)
2020-01-24 gw280@google.com Ensure GetFixturesPath works on Fuchsia (flutter/engine#15978)
2020-01-24 nurhan@google.com [web] Calling platform message callback after copy (flutter/engine#15950)
2020-01-24 iska.kaushik@gmail.com [fuchsia] Expose view_ref as part of dart:fuchsia initialization (flutter/engine#15958)
2020-01-24 gw280@google.com Refactor ShellTest to allow for different ShellTestPlatformViews (flutter/engine#15972)
2020-01-24 yjbanov@google.com Cache computed window.physicalSize in a FrameReference (flutter/engine#15955)
2020-01-24 dnfield@google.com the the fix (flutter/engine#15973)
2020-01-24 ferhat@gmail.com Optimize drawRRect to use dom_canvas (flutter/engine#15970)
2020-01-24 ferhat@gmail.com Remove paint apply in draw image (flutter/engine#15969)
2020-01-24 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/mac-amd64 from 6_pZp... to 7fqYj... (flutter/engine#15966)


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

-51a79649662f668eb73cdc042ec1eb80ffc7eb06
+4218f8026f2995de973564c6f6c6f3a419fec5ea