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

tests/language/src/InterfaceFactoryMultiTest.dart

Index: tests/language/src/InterfaceFactoryMultiTest.dart
===================================================================
--- tests/language/src/InterfaceFactoryMultiTest.dart	(revision 6413)
+++ tests/language/src/InterfaceFactoryMultiTest.dart	(working copy)
@@ -14,7 +14,7 @@
 class AImpl implements A {
   String _secret;
 
-  AImpl(String one, String two) : _secret = one + two;
+  AImpl(String one, String two) : _secret = "${one}${two}";
 
   String GetSecret() { return _secret; }
 }
@@ -28,7 +28,7 @@
 class BImpl implements B {
   String _secret;
 
-  BImpl(String one, String two) : _secret = two + one;
+  BImpl(String one, String two) : _secret = "${two}${one}";
 
   String GetSecret() { return _secret; }
 }