Control whether pub build and serve minify or not.

sdk/lib/_internal/pub/test/test_pub.dart

Index: sdk/lib/_internal/pub/test/test_pub.dart
diff --git a/sdk/lib/_internal/pub/test/test_pub.dart b/sdk/lib/_internal/pub/test/test_pub.dart
index 04ad649eafedf4c5bc8e4e74518c6f257b92b493..5da6eb62a3931ad7435b5e88d96068faea8fda38 100644
--- a/sdk/lib/_internal/pub/test/test_pub.dart
+++ b/sdk/lib/_internal/pub/test/test_pub.dart
@@ -56,6 +56,16 @@ final _requestedPaths = <String>[];
 /// The cached value for [_portCompleter].
 Completer<int> _portCompleterCache;
 
+/// A [Matcher] that matches JavaScript generated by dart2js with minification
+/// enabled.
+Matcher isMinifiedDart2JSOutput =
+    isNot(contains("// The code supports the following hooks"));
+
+/// A [Matcher] that matches JavaScript generated by dart2js with minification
+/// disabled.
+Matcher isUnminifiedDart2JSOutput =
+    contains("// The code supports the following hooks");
+
 /// The completer for [port].
 Completer<int> get _portCompleter {
   if (_portCompleterCache != null) return _portCompleterCache;