Starting making dart2js strong mode clean.

pkg/compiler/lib/src/native/behavior.dart

Index: pkg/compiler/lib/src/native/behavior.dart
diff --git a/pkg/compiler/lib/src/native/behavior.dart b/pkg/compiler/lib/src/native/behavior.dart
index 785f4cbe76fe1516a0f6116613ebd14ff12aed9b..3c950cc9e54d2ec935f0faf427feefbc786ebd36 100644
--- a/pkg/compiler/lib/src/native/behavior.dart
+++ b/pkg/compiler/lib/src/native/behavior.dart
@@ -523,14 +523,14 @@ class NativeBehavior {
       return new NativeBehavior();
     }
 
-    var specArgument = argNodes.head;
+    dynamic specArgument = argNodes.head;

[Emily Fortuna, 2017/06/14 17:42:51]

this should be type Node

[ahe, 2017/06/14 18:27:23]

That's what's inferred, but that type is not compatible with the assumption that
specArgument is a StringNode below.

What I'm trying to do here is go quickly through dart2js and make as small
changes as possible, and I think using dynamic is the safest way to that.
Someone can do another pass to remove dynamic, but consider that this code is
going to be replaced by the shared front-end.

[Emily Fortuna, 2017/06/14 18:29:05]

got it. thanks

     if (specArgument is! StringNode || specArgument.isInterpolation) {
       reporter.reportErrorMessage(
           specArgument, MessageKind.WRONG_ARGUMENT_FOR_JS_FIRST);
       return new NativeBehavior();
     }
 
-    var codeArgument = argNodes.tail.head;
+    dynamic codeArgument = argNodes.tail.head;

[Emily Fortuna, 2017/06/14 17:42:51]

same here

     if (codeArgument is! StringNode || codeArgument.isInterpolation) {
       reporter.reportErrorMessage(
           codeArgument, MessageKind.WRONG_ARGUMENT_FOR_JS_SECOND);