* Put generated kernel files into <build> directory

* USe default value for kernel file

* [kernel/flutter] Improve speed of first hot reload

* [kernel/flutter] Improve speed of first hot reload

* Revert "[kernel/flutter] Improve speed of first hot reload"

This reverts commit f3dc133878ec7405a8efb5715f1cfe720f4ea05f.

* Revert "[kernel/flutter] Improve speed of first hot reload"

This reverts commit f7bcb082b01cf9cf48f02c6aad9e5c79705def8f.

* Revert "Revert "[kernel/flutter] Improve speed of first hot reload""

This reverts commit 73c7a1a8e85a4c0397984d8b65a98b2f71bf84f3.

* [kernel/flutter] Improve speed of first hot reload

Do so by not evicting unnecessary paths (while still evicting paths
that was changed between the generation of the package file and the
initial upload).

* Fix grammar in method name

* Fix bad merge

* Add method to super class

* Use IKG for restarts, use IKG with ProtectedFileByteStore.

* Fix comment, add end of file newline.

* Remove unused import

* enable lint prefer_foreach

* fix tests

Syncing source files is not needed when host sends kernel file to the device.

* Keep incremental compiler state through full restart.

* Add todo

* Add todo

Reapply "When parts of the program are changed in a hot reload, but not executed during the reassemble, warn that a restart may be needed." (#12490)

This reverts commit 5e7bcbac.

`flutter run --benchmark` was triggering a different quick bailout path in the VM than `flutter run`. The failure has been fixed upstream.

* Fix restart flow for preview-dart-2 mode.

Restart in preview-dart-2 needs to use kernel file and it has to be complete, rather than incremental kernel file.

* Add curly braces

* Do full compile on restart

* Roll engine to pick up changes to hot reload for preview-dart-2

Revert "When parts of the program are changed in a hot reload, but not executed during the reassemble, warn that a restart may be needed. (#12304)" (#12406)

This reverts commit 90028813.

This change caused a few bots to fail with 'JSON-RPC error 110: Extension error', which is odd because _getUnusedChangesInLastReload is not an extension.

When parts of the program are changed in a hot reload, but not executed during the reassemble, warn that a restart may be needed. (#12304)

* round 3

* partially address comments

* merge

* review notes

* review

* review

* review

* Recreate outputFileName completer, handle process launch errors.

* Fix formatting

* Updated comment

This adds --preview-dart-2 flag that enables use of Dart 2.0 Frontend in Flutter tools.

Discovered dead code during review of #10791

* Do not lower-case paths during canonicalization.

This breaks hot reload on some platfroms with case insensitive file systems.

* Add unit tests

- [x] Catch SocketErrors and handle them gracefully.
- [x] Print 'Lost connection to device' when the service protocol connection is severed unexpectedly.
- [x] Print 'Application finished' when the application exits otherwise.

After this PR:

```
Launching lib/main.dart on Nexus 7 in debug mode...
Running 'gradle assembleDebug'...                     1.2s
Built build/app/outputs/apk/app-debug.apk (21.7MB).
Syncing files to device...
Application finished.
DevFS sync failed. Lost connection to device: SocketException: OS Error: Connection refused, errno = 111, address = 127.0.0.1, port = 53062
Could not perform initial file synchronization.
```

Fixes #6705

- [x] Skip scanning the file system if we already have the Dart dependency set.

Fixes #9376

```
Performing hot reload...
Reloaded 1 of 418 libraries in 888ms.

Performing hot reload...
Reloaded 1 of 418 libraries in 871ms.

** UNTAR dragontail under project root **
Performing hot reload...
Reloaded 0 of 418 libraries in 443ms.

** UNTAR dragontail under lib/ **
Performing hot reload...
Reloaded 0 of 418 libraries in 385ms.
```

Related #8876

* Print error message if a package is skipped during DevFS sync.

* review comments

* more review comments

* fix test

* [devFS] Use URI to represent paths on device

Previosuly, regular file paths in the format of the host platform were used to represent paths on device. That works when host and device share the same (POSIX) file path format. With a Windows host, this breaks. URIs are the solution as they are platform independent and the VM service on the device already interpreted the file paths as URIs anyways.

* review comments

* switch to file paths

* fix tests on Windows

* review comments

* Revert "Revert "Simplify path handling logic in dependency checker and devFS (#8414)" (#8467)"

This reverts commit 96ba7f76.

* Intentionally use a self-package URI in flutter_gallery

* tests to catch problems with self-package imports

This reverts commit e7bde11c.

Reason: broke hot reload when using "package:" style imports for sources
within the same project.

* Simplify path handling logic in dependency checker and devFS

Simplification will make it easier to port this to Windows.

* Roll Engine to 0a7b177c330367904597a6129b3eb653d29dfca0

This is a workaround to #8141