* enable Web Framework tests on try builds

* enable Web Framework tests only for some directories

No tests needed, since there is no change in functionality expected.

* creating test result directory. adding a prepare method to test runner

* addressing reviewer comments

Replaces the (temporary) compile-time option to pass engine switches
with the ability to pass them temporarily at runtime via environment
variables.

This is enabled only for debug/profile to avoid potential issues with
tampering with released applicaitons, but if there is a need for that in
the future it could be added (potentially with a whitelist, as is
currently used for Dart VM flags).

Windows portion of:
https://github.com/flutter/flutter/issues/38569
https://github.com/flutter/flutter/issues/60393

https://dart.googlesource.com/sdk.git/+log/c61a0818e4bd..2b8d00ac48e7

2020-09-22 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.10.0-156.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC dart-vm-team@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/+doc/master/autoroll/README.md

Registering the service worker immediately after the documented has loaded may cause SW initialization to compete with framework initialization. It was recommended to us that we defer the service worker setup until after the framework is done with setup, which should be sometime after the first frame.

To implement this, the binding will dispatch a platform message on startup. This can be listened for in the html document
#66066

* Make SkCanvas types @anonymous; reduce logging noise

* make SkParagraphBuilderNamespace anonymous

* make SkParagraphStyle anonymous