Allow user to specify mode for pub build/serve.

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

Index: sdk/lib/_internal/pub/test/transformer/dart2js/unminified_in_nonrelease_mode_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart b/sdk/lib/_internal/pub/test/transformer/dart2js/unminified_in_nonrelease_mode_test.dart
similarity index 84%
rename from sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart
rename to sdk/lib/_internal/pub/test/transformer/dart2js/unminified_in_nonrelease_mode_test.dart
index 1fc312c4fc6c9cc096368a5933fe764cfb34957f..dfffa2f8b6ec77a84ae89133805b819866db6a56 100644
--- a/sdk/lib/_internal/pub/test/transformer/dart2js/unminified_by_default_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/dart2js/unminified_in_nonrelease_mode_test.dart
@@ -10,7 +10,7 @@ import '../../serve/utils.dart';
 
 main() {
   initConfig();
-  integration("generates unminified JS by default", () {
+  integration("generates unminified JS when not in release mode", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("web", [
@@ -18,7 +18,7 @@ main() {
       ])
     ]).create();
 
-    pubServe();
+    pubServe(args: ["--mode", "whatever"]);
     requestShouldSucceed("main.dart.js", isUnminifiedDart2JSOutput);
     endPubServe();
   });