Control whether pub build and serve minify or not.

sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart

Index: sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_if_disabled_test.dart b/sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart
similarity index 78%
copy from sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_if_disabled_test.dart
copy to sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart
index fc9066755aa287f857f12e288335de93e2d2ebd2..3f0bb23832d48cfc2ca6192b0ace68da0bb92174 100644
--- a/sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_if_disabled_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart
@@ -10,7 +10,7 @@ import '../../serve/utils.dart';
 
 main() {
   initConfig();
-  integration("does not compile if dart2js is disabled", () {
+  integration("generates unminified JS by default", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("web", [
@@ -18,8 +18,8 @@ main() {
       ])
     ]).create();
 
-    startPubServe(dart2js: false);
-    requestShould404("main.dart.js");
+    startPubServe();
+    requestShouldSucceed("main.dart.js", isUnminifiedDart2JSOutput);
     endPubServe();
   });
 }