Rationalize coercions

test/dart_codegen/expect/d/d.dart

 library d;
 
 import 'a/a.dart' as DDC$a$;
 import 'package:dev_compiler/runtime/dart_logging_runtime.dart' as DEVC$RT;
 import 'b.dart';
 
 void foo() {
-  var x = f3(((__x0) => DEVC$RT.cast(__x0, dynamic, DDC$a$.A, "CastGeneral",
+  var x = f3(((__x0) => DEVC$RT.cast(__x0, dynamic, DDC$a$.A, "DynamicCast",
       """line 10, column 14 of test/dart_codegen/types/d.dart: """,
       __x0 is DDC$a$.A, true))(f4("""hello""")));
   var y = f1(DEVC$RT.wrap((dynamic f(dynamic __u2)) {
     dynamic c(dynamic x0) => ((__x1) => DEVC$RT.cast(__x1, dynamic, DDC$a$.A,
         "CastResult",
         """line 11, column 14 of test/dart_codegen/types/d.dart: """,
         __x1 is DDC$a$.A, true))(f(x0));
     return f == null ? null : c;
   }, f4, __t5, __t3, "Wrap",
       """line 11, column 14 of test/dart_codegen/types/d.dart: """,
       f4 is __t3));
   var z = f2(f3);
 }
 typedef DDC$a$.A __t3(DDC$a$.A __u4);
 typedef dynamic __t5(dynamic __u6);