Rework codegen tools to avoid relying on CWD; integrate with task model graph.

pkg/analyzer/tool/task_dependency_graph/check_test.dart

Index: pkg/analyzer/tool/task_dependency_graph/check_test.dart
diff --git a/pkg/analyzer/tool/task_dependency_graph/check_test.dart b/pkg/analyzer/tool/task_dependency_graph/check_test.dart
index a2d1118b1393c4be89acaf8132cc9d349d98b4b8..b64bf521c5c6948a80902e76f75d57d959bcec38 100644
--- a/pkg/analyzer/tool/task_dependency_graph/check_test.dart
+++ b/pkg/analyzer/tool/task_dependency_graph/check_test.dart
@@ -16,9 +16,10 @@ import 'generate.dart';
  */
 main() {
   String script = Platform.script.toFilePath(windows: Platform.isWindows);
-  Driver driver = new Driver();
-  if (!driver.checkFile()) {
-    print('${driver.file.absolute} does not have expected contents.');
+  String pkgPath = normalize(join(dirname(script), '..', '..'));
+  if (!target.check(pkgPath)) {
+    print(
+        '${target.output(pkgPath).absolute} does not have expected contents.');
     print('Please regenerate using:');
     String executable = Platform.executable;
     String packageRoot = '';