Introduce sky/unit/test

This patch adds a new test harness and a first, trivial test to run with the
harness. The new test harness is built on package:test and should run on
Travis. Over time, we'll migrate our existing tests into this harness.

packages/flutter/pubspec.yaml

@@ -11,7 +11,7 @@ dependencies:
   newton: ^0.1.2
   sky_engine: ^0.0.12
   sky_services: ^0.0.12
-  sky_tools: ^0.0.9
+  sky_tools: ^0.0.10
   vector_math: ^1.4.3
 environment:
   sdk: '>=1.8.0 <2.0.0'

packages/unit/.gitignore

+.pub
+packages
+pubspec.lock

packages/unit/pubspec.yaml

+name: sky_unit_tests
+dependencies:
+  sky: any
+  sky_tools: any
+  test: any
+dependency_overrides:
+  material_design_icons:
+    path: ../packages/material_design_icons
+  sky:
+    path: ../packages/sky

packages/unit/test/harness/trivial_test.dart

+import 'package:test/test.dart';
+
+void main() {
+  test("should pass", () {
+    expect(1 + 1, equals(2));
+  });
+}