Checkpoint for Response and Tracer: most tests passing.
More tests working.
Work on tracing ending.
Transform tests are passing.
Error tests passing.
Branching tests pass.
All tests passing.
Merge branch 'master' into tracing

Conflicts:
	lib/runtime/cache.dart
	lib/runtime/transforms.dart
	test/generated/addendum_test.dart
	test/generated/schema_unknown_fields_client.dart
Starting to fit tracing into Multiplexer.
Const factories.
Merge branch 'tracing' into tracing-2
Multiplexer tracing events.
Proxy trace event.
Migrate from dart:json to json pub package
Fixes, patches, upgrades, etc.
Fix signature of shuffle in _ObservableImmutableListView
Track async operations.
Request template fixes.
Upgrade to the latest libs and fix API breakages
Merge pull request #113 from yjbanov/json-package-migration

Upgrade to the latest SDK and 3rd-party libs and fix API breakages