Ensure apidoc exits with non-zero exit code when dart2js crashes.

dart/utils/apidoc/apidoc.dart

Index: dart/utils/apidoc/apidoc.dart
diff --git a/dart/utils/apidoc/apidoc.dart b/dart/utils/apidoc/apidoc.dart
index 5405e3a7233c26f995614c55be3e409a7bb3a8cf..8b1258245eb13c7c6344908e9772ed8cac4c66cf 100644
--- a/dart/utils/apidoc/apidoc.dart
+++ b/dart/utils/apidoc/apidoc.dart
@@ -150,7 +150,11 @@ void main() {
       .then((_) => apidoc.documentLibraries(apidocLibraries, libPath, pkgPath))
       .then((_) => compileScript(mode, outputDir, libPath))
       .then((_) => print(apidoc.status))
-      .catchError((e) => print('Error: generation failed: ${e.error}'))
+      .catchError((e) {
+        print('Error: generation failed: ${e}');
+        apidoc.cleanup();
+        exit(1);
+      })
       .whenComplete(() => apidoc.cleanup());
   });
 }