Also includes
  * Updates to affected tests
  * Change flutter_tools to pass package URIs to the Dart front end
    instead of filesystem paths

This reverts commit ca0487b9.

* Roll engine to 4c79e423dc6f89f98d8ceb263a5ca78e2f2da996 and update tests

* Switch to URIs for breakpoints and unskip tests on Windows

addBreakpointWithScriptUri expects Uris. By coincidence, FS paths work on Mac/Linux but they fail on Windows. One of the issues in the skip comment is fixed, the other one seems not relevant here.

* Apply symlink resolution to all integration tests

The default temp folders we get include symlinks which breaks breakpoints.

* Save 

* Fix typo

This reverts commit a34488dd.

aed6b8c46 Roll Dart to ac6d4f7e653deba11d4836768376537893a9e9d6. (#6549)
3ba6270b2 Roll src/third_party/skia 921ec976556c..4b7b2ceb4ad9 (14 commits) (#6550)

* Change file paths to URIs to fix "Could not run configuration in engine" on Windows

Plus unskip test that was failing due to this.

Fixes #21348.

* Remove unused import

Underlying issue with breakpoint was that /var path is a symlink to a /private/var on mac. Because of that breakpoint could not be resolved.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Unskip integration tests on Windows that now pass

The referenced issue is closed and these tests pass for me locally on Windows now.

* Remove import that's no longer used

* Add another issue that is afffecting these tests on Windows

* Add a hot restart test and mark skip on Windows

Skipped due to https://github.com/flutter/flutter/issues/21348.

* Pass uri instead of filepaths when hot-reloading.

Bug: https://github.com/flutter/flutter/issues/21168

* Remove imports. Enable another test

* Restore skipping of test on mac

* Unskip expression evaluation integration tests for non-Windows

* Add additional into to skip comments

* Add missing import

Due to CPU contention we've seen these go really slow on Cirrus (see https://github.com/flutter/flutter/issues/19542#issuecomment-414265152), and there's also a chance our flakes are timeouts due to running slow rather than hanging.

All temporary directory start with `flutter_` and have their random component separated from the name by a period, as in `flutter_test_bundle.YFYQMY`.

I've tried to find some of the places where we didn't cleanly delete temporary directories, too. This greatly reduces, though it does not entirely eliminate, the directories we leave behind when running tests, especially `flutter_tools` tests.

While I was at it I standardized on `tempDir` as the variable name for temporary directories, since it was the most common, removing occurrences of `temp` and `tmp`, among others.

Also I factored out some common code that used to catch exceptions that happen on Windows, and made more places use that pattern.

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

* Skip tests instead of expecting failure, because expected failure = timeout which is slow

Some of these tests are known to fail and were coded to expect it; however because the failure is a timeout it's just dragging out test runs (shortening timeouts will make the tests flakier).

* Make it easier to find skipped tests

* Change SKIP to TODO

* Rename util -> test_utils

* Rename flutter_test_driver -> test_driver

* Switch testWithContext -> test

* Remove unused import

* Move test project into a class to make it easier to have multiple of these

Each "TestProject" class can contain its files and things like named breakpoint locations.

* Split expression evaluation tests into own file

* Include last response in error messages

* Update expectations based on current bugs

* Fix async-ness in tests

* Fix incorrect expectation in test

* Fix incorrect evaluations

* Remove skips for tests that are now passing on master

* Expect pass on Linux

‍♂️

* Call the code

* Skip expression evaluation tests on Windows

* Skip whole group, not just one test

* Remove duplicated method from merge

* Fix misplaced close of group

* Remove code that was duplicated from test we copied

Not sure how this ended up in here?

* Re-fix typo