[ci] Add Windows Dart unit tests (#1794)

.ci.yaml

@@ -36,6 +36,20 @@ targets:
           {"dependency": "vs_build"}
         ]
 
+  - name: Windows dart_unit_tests master - packages
+    recipe: packages/packages
+    timeout: 30
+    bringup: true
+    properties:
+      add_recipes_cq: "true"
+      target_file: windows_dart_unit_tests.yaml
+      channel: master
+      version_file: flutter_master.version
+      dependencies: >
+        [
+          {"dependency": "vs_build"}
+        ]
+
   - name: Windows win32-platform_tests master - packages
     recipe: packages/packages
     timeout: 30

.ci/scripts/dart_unit_tests.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+dart pub global run flutter_plugin_tools test --packages-for-branch \
+  --log-timing

.ci/targets/windows_dart_unit_tests.yaml

@@ -0,0 +1,5 @@
+tasks:
+  - name: prepare tool
+    script: .ci/scripts/prepare_tool.sh
+  - name: custom package tests
+    script: .ci/scripts/dart_unit_tests.sh