Fix analysis shard of dev/bots/test.dart so it works on Windows. (#21203)

Normalize file path to non-Windows so string path comparison works.

dev/bots/analyze.dart

@@ -249,7 +249,8 @@ Future<Null> _verifyNoTestPackageImports(String workingDirectory) async {
     })
     .map<String>((FileSystemEntity entity) {
       final File file = entity;
-      final String name = path.relative(file.path, from: workingDirectory);
+      final String name = Uri.file(path.relative(file.path,
+          from: workingDirectory)).toFilePath(windows: false);
       if (name.startsWith('bin/cache') ||
           name == 'dev/bots/test.dart' ||
           name.startsWith('.pub-cache'))
@@ -266,7 +267,7 @@ Future<Null> _verifyNoTestPackageImports(String workingDirectory) async {
           return '  $name: Shim seems to be missing the expected import/export lines.';
         }
         final int count = 'package:test'.allMatches(data).length;
-        if (file.path.contains('/test_driver/') ||
+        if (path.split(file.path).contains('test_driver') ||
             name.startsWith('dev/missing_dependency_tests/') ||
             name.startsWith('dev/automated_tests/') ||
             name.startsWith('packages/flutter/test/engine/') ||