Put in a teardown for the docs test, fixed dom.py to actually run it correctly, added PRESUMBIT.

tools/dom/docs/test/docs_test.dart

Index: tools/dom/docs/test/docs_test.dart
diff --git a/tools/dom/docs/test/docs_test.dart b/tools/dom/docs/test/docs_test.dart
index e87b2f6f4f93af8666efe4bace714d9694d5dbbd..3133fe79159f66a2bd57855be21520c3b76d5788 100644
--- a/tools/dom/docs/test/docs_test.dart
+++ b/tools/dom/docs/test/docs_test.dart
@@ -14,38 +14,42 @@ import '../lib/docs.dart';
 final testJsonPath = scriptDir.append('test.json').canonicalize();
 
 main() {
-  test('Ensure that docs.json is up to date', () {
+  group('docs', () {
     var oldJson = new File.fromPath(json_path);
     var testJson = new File.fromPath(testJsonPath);
 
-    // We should find a json file where we expect it.
-    expect(oldJson.existsSync(), isTrue);
+    tearDown(() {
+      // Clean up.
+      if (testJson.existsSync()) {
+        testJson.deleteSync();
+      }
+      assert(!testJson.existsSync());
+    });
 
-    // Save the last modified time to check it at the end.
-    var oldJsonModified = oldJson.lastModifiedSync();
+    test('Ensure that docs.json is up to date', () {
+      // We should find a json file where we expect it.
+      expect(oldJson.existsSync(), isTrue);
 
-    // There should be no test file yet.
-    if (testJson.existsSync()) testJson.deleteSync();
-    expect(testJson.existsSync(), isFalse);
+      // Save the last modified time to check it at the end.
+      var oldJsonModified = oldJson.lastModifiedSync();
 
-    expect(convert(lib_path, testJsonPath)
-        .then((bool anyErrors) {
-      expect(anyErrors, isFalse);
+      // There should be no test file yet.
+      if (testJson.existsSync()) testJson.deleteSync();
+      assert(!testJson.existsSync());
 
-      // We should have a file now.
-      expect(testJson.existsSync(), isTrue);
+      expect(convert(lib_path, testJsonPath)
+          .then((bool anyErrors) {
+        expect(anyErrors, isFalse);
 
-      // Ensure that there's nothing different between the new JSON and old.
-      expect(testJson.readAsStringSync(), equals(oldJson.readAsStringSync()));
+        // We should have a file now.
+        expect(testJson.existsSync(), isTrue);
 
-      // Ensure that the old JSON file didn't actually change.
-      expect(oldJsonModified, equals(oldJson.lastModifiedSync()));
+        // Ensure that there's nothing different between the new JSON and old.
+        expect(testJson.readAsStringSync(), equals(oldJson.readAsStringSync()));
 
-      // Clean up.
-      if (testJson.existsSync()) {
-        testJson.deleteSync();
-      }
-      expect(testJson.existsSync(), isFalse);
-    }), completes);
+        // Ensure that the old JSON file didn't actually change.
+        expect(oldJsonModified, equals(oldJson.lastModifiedSync()));
+      }), completes);
+    });
   });
 }