Rationalize coercions

test/dart_codegen/expect/types.txt

Index: test/dart_codegen/expect/types.txt
diff --git a/test/dart_codegen/expect/types.txt b/test/dart_codegen/expect/types.txt
index f0ef1553ae7204fea25c32b9d33cf3b1213ed69d..a66fd96cb4572283635a409a05908aaa40ea8321 100644
--- a/test/dart_codegen/expect/types.txt
+++ b/test/dart_codegen/expect/types.txt
@@ -1,11 +1,11 @@
 // Messages from compiling types.dart
-info: line 10, column 6 of test/dart_codegen/types/c.dart: [DownCast] f4(3) (dynamic) will need runtime check to cast to type A
+info: line 10, column 6 of test/dart_codegen/types/c.dart: [DynamicCast] f4(3) (dynamic) will need runtime check to cast to type A
   f3(f4(3));
      ^^^^^
 warning: line 11, column 6 of test/dart_codegen/types/c.dart: [ClosureWrap] f4 ((dynamic) → dynamic) will need to be wrapped with a closure of type (A) → A
   f1(f4);
      ^^
-info: line 10, column 14 of test/dart_codegen/types/d.dart: [DownCast] f4("""hello""") (dynamic) will need runtime check to cast to type A
+info: line 10, column 14 of test/dart_codegen/types/d.dart: [DynamicCast] f4("""hello""") (dynamic) will need runtime check to cast to type A
   var x = f3(f4("""hello"""));
              ^^^^^^^^^^^^^^^
 warning: line 11, column 14 of test/dart_codegen/types/d.dart: [ClosureWrap] f4 ((dynamic) → dynamic) will need to be wrapped with a closure of type (A) → A