fix #30094, assert should work with a function

tests/language_strong/assert_with_message_test.dart

Index: tests/language_strong/assert_with_message_test.dart
diff --git a/tests/language_strong/assert_with_message_test.dart b/tests/language_strong/assert_with_message_test.dart
index 878bd712627091f9300f30579c70df4939992358..147ee2fb6e6da13a8fe69a7501eed81ccb1b1ce4 100644
--- a/tests/language_strong/assert_with_message_test.dart
+++ b/tests/language_strong/assert_with_message_test.dart
@@ -52,7 +52,7 @@ testNullMessage() {
     assert(false, null);
     Expect.fail("Assert should throw.");
   } catch (e) {
-    Expect.isTrue(e.toString().contains("null"));
+    Expect.isTrue(e.toString().contains("is not true"));

[Jennifer Messerly, 2017/07/07 23:43:17]

this test now matches VM behavior

   }
 }
 
@@ -82,7 +82,7 @@ testCallsToStringOnMessageLazily() {
     Expect.fail("Assert should throw.");
   } catch (e) {
     Expect.isFalse(toString.calledToString);
-    Expect.isTrue(e.toString().contains("toString!"));
-    Expect.isTrue(toString.calledToString);
+    Expect.isTrue(e.toString().contains("Instance of 'ToString'"));

[Jennifer Messerly, 2017/07/07 23:43:17]

same here

+    Expect.isFalse(toString.calledToString);
   }
 }