fixes #206, add checking for unary ops

lib/runtime/dart/convert.js

Index: lib/runtime/dart/convert.js
diff --git a/lib/runtime/dart/convert.js b/lib/runtime/dart/convert.js
index 4ff12edfdb7645f2f13511ca154430a124f0429c..5721a75a96889e63431d22be5d8fb66f97aed2f7 100644
--- a/lib/runtime/dart/convert.js
+++ b/lib/runtime/dart/convert.js
@@ -1204,7 +1204,7 @@ var collection = dart.import(collection);
     }
     writeJsonValue(object) {
       if (dart.is(object, core.num)) {
-        if (dart.dsend(dart.dload(object, 'isFinite'), '!'))
+        if (!dart.notNull(dart.as(dart.dload(object, 'isFinite'), core.bool)))

[Jennifer Messerly, 2015/06/04 00:16:23]

we'll probably want to do something about the nonNull as bool pattern of checks
...

           return false;
         this.writeNumber(dart.as(object, core.num));
         return true;