Register toString dynamic invocation in the presence of string interpolation.

tests/compiler/dart2js/call_site_type_inferer_test.dart

Index: tests/compiler/dart2js/call_site_type_inferer_test.dart
diff --git a/tests/compiler/dart2js/call_site_type_inferer_test.dart b/tests/compiler/dart2js/call_site_type_inferer_test.dart
index 418948dbc2487cdf82bc9610dcd6fc1cd6a32cde..704cba584695580d30974f941284d8cef96b9112 100644
--- a/tests/compiler/dart2js/call_site_type_inferer_test.dart
+++ b/tests/compiler/dart2js/call_site_type_inferer_test.dart
@@ -9,12 +9,6 @@
 #import('compiler_helper.dart');
 #import('parser_helper.dart');
 
-findElement(var compiler, String name) {
-  var element = compiler.mainApp.find(buildSourceString(name));
-  Expect.isNotNull(element, 'Could not locate $name.');
-  return element;
-}
-
 void compileAndFind(String code,
                     String className,
                     String memberName,