* rename service_protocol.dart to protocol_discovery.dart

* add a wrapper around the obs. protocol

* use json-rpc in run

* consolidate obs. code; implement flutter run --benchmark

* review comments

Artifacts from local engine builds will be found based on the --local-engine flag

It's safe to remove the unneeded `void`s from setters since the blocking issues in the
`always_declare_return_types` lint have been fixed (https://github.com/dart-lang/linter/).  We can also safely flip the bit on  `avoid_return_types_on_setters`.

Host tools can be found in the artifact cache directory for the host platform.
If a developer wants to use a local engine build instead, then provide an
--engine-build flag that selects the specific engine build variant.

* be more lenient when looking for matching android sdk components

* use a null aware operator

* complain on missing entries in flutter.yaml

* change to a hard failure

* better parsing of adb devices output

* re-order lines

* fix analysis errors

* review comments; fix test

* re-add an export for debugPrint

Check the adb install output for errors and stop "flutter run" if package installation fails (#3672)

* rework flutter run

* fix npe with --debug-port

* connect to obs and exit when that conneciton closes

* update todos

* add a target for android-x64

* update armeabi-v7a to x86_64

Also, update hello_android to use the new Java class names.

Add a command that can capture a Skia picture of a Flutter frame and send it to a file or skiaserve debugger (#3165)

Support "flutter refresh" in the Gradle-based sample project

Well, all the easy ones, anyway.

For some reason `// ignore:` isn't working for me so I've disabled
lints that need that. Also disabled those that require a ton of work
(which I'm doing, but not in this PR, to keep it reviewable).

This adds:
- avoid_init_to_null
- library_names
- package_api_docs
- package_names
- package_prefixed_library_names
- prefer_is_not_empty
- sort_constructors_first
- sort_unnamed_constructors_first
- unnecessary_getters_setters