- Fix use of String operator + in language and corelib tests.

tests/language/src/InterfaceFactoryTest.dart

Index: tests/language/src/InterfaceFactoryTest.dart
===================================================================
--- tests/language/src/InterfaceFactoryTest.dart	(revision 6413)
+++ tests/language/src/InterfaceFactoryTest.dart	(working copy)
@@ -42,7 +42,7 @@
 class SomeImplementation implements Interface2 {
   String _secret;
 
-  SomeImplementation(String one, String two) : _secret = one + two {}
+  SomeImplementation(String one, String two) : _secret = "${one}${two}" {}
 
   String GetSecret() { return _secret; }
 }