allow JS builtin to be typed as needed

lib/src/codegen/reify_coercions.dart

Index: lib/src/codegen/reify_coercions.dart
diff --git a/lib/src/codegen/reify_coercions.dart b/lib/src/codegen/reify_coercions.dart
index 36c965e3fbd46383b701590f411c41eb3a075a78..3aead3ebf0403b7717d9f31dffb2838f6308e54a 100644
--- a/lib/src/codegen/reify_coercions.dart
+++ b/lib/src/codegen/reify_coercions.dart
@@ -12,6 +12,7 @@ import 'package:analyzer/src/generated/type_system.dart'
 import 'package:logging/logging.dart' as logger;
 
 import '../info.dart';
+import '../utils.dart' show isInlineJS;
 
 import 'ast_builder.dart';
 
@@ -168,6 +169,10 @@ class CoercionManager {
       Expression inner = coerceExpression(e.expression, c);
       return new NamedExpression(e.name, inner);
     }
+    if (e is MethodInvocation && isInlineJS(e.methodName.staticElement)) {
+      // Inline JS code should not need casts.
+      return e;
+    }
     if (c is Cast) return _castExpression(e, c);
     assert(c is Identity);
     return e;