Finish strong mode cleaning of dart2js.

pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart

Index: pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
diff --git a/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart b/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
index 9ae3b434163bc7e188578f4da23867c366f4554a..7f5514290aa48ba3d7a6cebb8f8053672b0923c5 100644
--- a/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
@@ -18,7 +18,7 @@ class ClassBuilder {
 
   jsAst.Name superName;
   jsAst.Node functionType;
-  List<jsAst.Node> fieldMetadata;
+  List<jsAst.Expression> fieldMetadata;

[ahe, 2017/06/15 09:36:39]

I'm concerned about causing a checked mode problem.

[Johnni Winther, 2017/06/15 10:21:26]

If you change `var fieldMetadata = [];` in class_emitter line 128 to ` var
fieldMetadata = <Expression>[];` it should be fine.

[ahe, 2017/06/15 11:41:57]

Done.

 
   final Entity element;
   final Namer namer;
@@ -75,7 +75,7 @@ class ClassBuilder {
     }
     // See [fieldEncodingDescription] above.
     parts.addAll(js.joinLiterals(fields, js.stringPart(',')));
-    var classData = js.concatenateStrings(parts, addQuotes: true);
+    dynamic classData = js.concatenateStrings(parts, addQuotes: true);
     if (fieldMetadata != null) {
       // If we need to store fieldMetadata, classData is turned into an array,
       // and the field metadata is appended. So if classData is just a string,