Add an extension point for contributing to HTML_ERRORS.

pkg/analyzer/test/src/task/html_test.dart

Index: pkg/analyzer/test/src/task/html_test.dart
diff --git a/pkg/analyzer/test/src/task/html_test.dart b/pkg/analyzer/test/src/task/html_test.dart
index ec78be15093b85ba9f5c8d3d6758114f67cf2c3e..a07dc75135e409317615f1adb71811359393e312 100644
--- a/pkg/analyzer/test/src/task/html_test.dart
+++ b/pkg/analyzer/test/src/task/html_test.dart
@@ -175,18 +175,6 @@ class DartScriptsTaskTest extends AbstractContextTest {
 
 @reflectiveTest
 class HtmlErrorsTaskTest extends AbstractContextTest {
-  test_buildInputs() {
-    Source source = newSource('/test.html');
-    Map<String, TaskInput> inputs = HtmlErrorsTask.buildInputs(source);
-    expect(inputs, isNotNull);
-    expect(
-        inputs.keys,
-        unorderedEquals([
-          HtmlErrorsTask.DART_ERRORS_INPUT,
-          HtmlErrorsTask.DOCUMENT_ERRORS_INPUT
-        ]));
-  }
-
   test_constructor() {
     Source source = newSource('/test.html');
     HtmlErrorsTask task = new HtmlErrorsTask(context, source);