* Moved the default BinaryMessenger instance to ServicesBinding

This reverts commit 821602ae.

* Added assertion in defaultBinaryMessenger. Also fixed the devicelab tests.

This reverts commit 92ef2b9c.

This requires either runApp() or
WidgetsFlutterBinding.ensureInitialized() to have been called before
using any MethodChannels. Plugins broadly rely on MethodChannels and
right now there's no general requirements that they be constructed
within the runApp call, so the ecosystem breakages from this are broader
than originally thought. Reverting for now.

* 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

Channels don't preserve Map and List type arguments: Map<String, Object>
arrives as Map<dynamic, dynamic> to the receiver.

In Dart 2 type system dynamic no longer serves as bottom type so
Map<dynamic, dynamic> can't be assign to a variable of type
Map<String, dynamic>.

Issue #14556

Small code changes as part of moving the framework SDK forward to a 2.0 dev version.