partially implement instance of checks and some codegen fixes

lib/src/js/precedence.dart

Index: lib/src/js/precedence.dart
diff --git a/lib/src/js/precedence.dart b/lib/src/js/precedence.dart
index 6d66f1fca5a74c22b24aad9058cede3588202aed..d63253e1d395c2b1d818382556adc8241949a562 100644
--- a/lib/src/js/precedence.dart
+++ b/lib/src/js/precedence.dart
@@ -18,8 +18,7 @@ const ADDITIVE = SHIFT + 1;
 const MULTIPLICATIVE = ADDITIVE + 1;
 const UNARY = MULTIPLICATIVE + 1;
 const LEFT_HAND_SIDE = UNARY + 1;
-// We merge new, call and member expressions.
-// This means that we have to emit parenthesis for 'new's. For example `new X;`
-// should be printed as `new X();`. This simplifies the requirements.
 const CALL = LEFT_HAND_SIDE;
-const PRIMARY = CALL + 1;
+// We always emit `new` with parenthesis, so it uses ACCESS as its precedence.
+const ACCESS = CALL + 1;
+const PRIMARY = ACCESS + 1;