Seems like we don't yet run the flutter tests on Windows, but we're
close to being able to. This makes some minor changes to make that
more possible:

 - fix the stack parsing code to support Windows paths
 - fix the tests for the stack error handling code to handle Windows paths
 - skip some tests that rely on Ahem font metrics

* Revert "Revert "Make artifact downloading more robust for flaky networks" (#13995)"

This reverts commit 33d8a035.

* Use subdirectories to organize cached files

* Fix unauthorized import

renderObject.setFlatChildren expects List<RenderBox>, not List<RenderObject>.

...especially about TextDirection.

* Clean up output directory before copying over new files

* Use standard clean task command

* JSON.decode produces Map<String, dynamic> and List<dynamic>
objects. If a more tight type is required then object needs to
be converted explicitly (see dart-lang/sdk#31876);
* Completer<dynamic> produces Future<dynamic>. In Dart 2 it is
runtime error to assign Future<dynamic> to variable of type Future<T>;

If the downloaded file is an actual SKP and not an error report, then the
default UTF-8 codec will fail to decode the SKP content

This CL also refactors common logic for RenderPhysicalModel and
RenderPhysicalShape into a base class _RenderPhysicalModelBase.

Apple encodes syslog entries using a 7-bit encoding where input UTF-8 bytes
are encoded as follows:
1. 0x00 to 0x19: non-printing range. Some ignored, some encoded as <...>.
2. 0x20 to 0x7f: as-is, with the exception of 0x5c (backslash).
3. 0x5c (backslash): octal representation \134.
4. 0x80 to 0x9f: \M^x (using control-character notation for range 0x00 to 0x40).
5. 0xa0: octal representation \240.
6. 0xa1 to 0xf7: \M-x (where x is the input byte stripped of its high-order bit).
7. 0xf8 to 0xff: unused in 4-byte UTF-8.

As there doesn't appear to be a system tool to decode these strings, we
implement here in Dart. If we're unable to decode a string (e.g.
decoding results in an invalid UTF-8 string), we fall back to emitting
the log line as-is.

Just download a Flutter ZIP bundle, unzip, and double-click on `flutter_console.bat` to get started. No PATH modifications required.

And add a test that catches these problems.

This gets us back to where we were a few minutes ago.

This reverts commit 592f2979.

* Revive "Push physical layers with paths instead of rects in RenderPhysicalModel. (#13942)"

That commit was reverted due to a performance problem which has now been
fixed.

* Roll engine 05fe72d068e19c7886e8d27f9b004201d5ad1300

Fixes https://github.com/flutter/flutter/issues/14058.

* Reland 9534082f with fix for incremental compilation.

When in incremental mode, awaiting exitCode won't work because compiler is not expected to exit after compilation.
Instead listen for stdout stream closing and report error if outputFilename has not been received.

* Fix lints

* Fix handling --preview-dart-2 for ios

* final var

* send 'reloadRecommended' info to IDEs

* rename hint ==> hintMessage

* Remove mention of --assert-initializer from CONTRIBUTING.md
* Remove options variable as well

This reverts commit 9534082f.

Causes hot_mode_dev_cycle__preview_dart_2_benchmark test timeout.

* Check frontend_server exit code.

When frontend_server completes abnormally, flutter tools has to stop and let user know.

* Add tests