Add support for metadata on type variables to Fasta parser.

pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart

Index: pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
index 13d66e335e398262b19706165c4c22c2c1e5cb25..890f66cc39f858a2243014d80414d2f4f2fae161 100644
--- a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
+++ b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
@@ -162,6 +162,17 @@ class AstBuilder extends ScopeListener {
     push(ast.methodInvocation(null, null, null, null, arguments));
   }
 
+  void endMetadata(Token beginToken, Token periodBeforeName, Token endToken) {
+    debugEvent("Metadata");
+    ArgumentList arguments = pop();
+    SimpleIdentifier constructorName = popIfNotNull(periodBeforeName);
+    var typeArguments = pop();
+    assert(typeArguments == null); // TODO(paulberry)
+    Identifier name = pop();
+    push(ast.annotation(toAnalyzerToken(beginToken), name,
+        toAnalyzerToken(periodBeforeName), constructorName, arguments));
+  }
+
   void handleIdentifier(Token token, IdentifierContext context) {
     debugEvent("handleIdentifier");
     analyzer.Token analyzerToken = toAnalyzerToken(token);
@@ -1204,9 +1215,8 @@ class AstBuilder extends ScopeListener {
     debugEvent("TypeVariable");
     TypeAnnotation bound = pop();
     SimpleIdentifier name = pop();
-    List<Annotation> metadata = null; // TODO(paulberry)
-    // TODO(paulberry): capture doc comments.  See dartbug.com/28851.
-    Comment comment = null;
+    List<Annotation> metadata = pop();
+    Comment comment = pop();
     push(ast.typeParameter(
         comment, metadata, name, toAnalyzerToken(extendsOrSuper), bound));
   }