Add the generator and the generated files

pkg/analyzer_plugin/tool/spec/codegen_dart.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'api.dart';
+
+/**
+ * Visitor specialized for generating Dart code.
+ */
+class DartCodegenVisitor extends HierarchicalApiVisitor {
+  /**
+   * Type references in the spec that are named something else in Dart.
+   */
+  static const Map<String, String> _typeRenames = const {
+    'long': 'int',
+    'object': 'Map',
+  };
+
+  DartCodegenVisitor(Api api) : super(api);
+
+  /**
+   * Convert the given [TypeDecl] to a Dart type.
+   */
+  String dartType(TypeDecl type) {
+    if (type is TypeReference) {
+      String typeName = type.typeName;
+      TypeDefinition referencedDefinition = api.types[typeName];
+      if (_typeRenames.containsKey(typeName)) {
+        return _typeRenames[typeName];
+      }
+      if (referencedDefinition == null) {
+        return typeName;
+      }
+      TypeDecl referencedType = referencedDefinition.type;
+      if (referencedType is TypeObject || referencedType is TypeEnum) {
+        return typeName;
+      }
+      return dartType(referencedType);
+    } else if (type is TypeList) {
+      return 'List<${dartType(type.itemType)}>';
+    } else if (type is TypeMap) {
+      return 'Map<${dartType(type.keyType)}, ${dartType(type.valueType)}>';
+    } else if (type is TypeUnion) {
+      return 'dynamic';
+    } else {
+      throw new Exception("Can't convert to a dart type");
+    }
+  }
+}