* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

These are essentially self-inflicted race conditions. Instead of timeouts we're going to try a more verbose logging mechanism that points out when things are taking a long time.

* Fix `flutter test`e xpression eval tests

We weren't passing `beforeStart` through so the breakpoints were never being set, which means the evaluations were happening while the code was running.

* Ensure we wait for breakpoints before trying to evaluate

* Add some basic tests for evaluating expressions in `flutter test`

* Review tweaks

This reverts commit 76f70810.

* Remove many timeouts.

These are essentially self-inflicted race conditions. Instead of timeouts we're going to try a more verbose logging mechanism that points out when things are taking a long time.

* Get the attach tests to pass.

* Apply review comments from Todd

* More review comment fixes

* Put back the extended timeouts here now that I know why we have them...

* Refactor Test Driver in preperation for `flutter test` integration tests

* Fix indent

* 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

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

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.

* Reland "Roll engine to version b148e628ec86b3a9a0382e0bcfae73f0390a8232 (#20427)"

This is a re-land with downgraded `package:flutter_gallery_assets`
version.

* Downgrade package:flutter_gallery_assets to 0.1.4

* Change engine.version to 81baff97c29bb08cbf8453a3f9042c5813f84ad3 (which contains an additional fix)

* Change engine.version to e3687f70c7ece72000b32ee1b3c02755ba5361ac (since mac tarballs are corrupted on earlier commit)

Reason for revert: The package:flutter_gallery_assets has removed some images which are required for the examples/flutter_gallery, so the gallery build is failing (only discovered after landing, since gallery doesn't seem to get built during github PR presubmit checks)

This CL

  * rolls `engine.version` to flutter/engine@b148e628 (which includes dart sdk 2.1.0-dev)
  * rolls `goldens.version` to flutter/goldens@6c45fafdf (which includes updates due to skia changes in engine)
  * changes `platform.dill` to `platform_strong.dill` in various places due to flutter/engine@a84b210b
  * adds explicit `environment: sdk: ">=2.0.0-dev.68 < 3.0.0"` constraints to `pubspec.yaml` and `pubspec.yaml.tmpl` files (since pub defaults to `<2.0.0` if omitted) 
  * upgrades to newer versions of various 3rd party packages (to ensure transitive dependencies have `<3.0.0` sdk constraint)

* Look up breakpoints rather than relying on magic numbers

* Make breakpoint comment more obvious

* 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