Clean up some warnings and deprecated calls.

utils/tests/pub/command_line_config.dart

Index: utils/tests/pub/command_line_config.dart
diff --git a/utils/tests/pub/command_line_config.dart b/utils/tests/pub/command_line_config.dart
index d15126bcb7cce30e33c8686294e9deb2b0d41b6c..b7b7b34e74f1ac2e28432f3e02559dc83374370f 100644
--- a/utils/tests/pub/command_line_config.dart
+++ b/utils/tests/pub/command_line_config.dart
@@ -116,7 +116,7 @@ class CommandLineConfiguration extends Configuration {
   String _indent(String str) {
     // TODO(nweiz): Use this simpler code once issue 2980 is fixed.
     // return str.replaceAll(new RegExp("^", multiLine: true), "  ");
-    return Strings.join(str.split("\n").map((line) => "  $line"), "\n");
+    return str.split("\n").map((line) => "  $line").join("\n");
   }
 }