Handle for-in loops

lib/runtime/dart/_interceptors.js

Index: lib/runtime/dart/_interceptors.js
diff --git a/lib/runtime/dart/_interceptors.js b/lib/runtime/dart/_interceptors.js
index a57f1342d03af83ff691c0d03e339dd306c7686a..bf9881bc82233e36721ab88123263fef99796d3a 100644
--- a/lib/runtime/dart/_interceptors.js
+++ b/lib/runtime/dart/_interceptors.js
@@ -857,8 +857,8 @@ var _interceptors;
       let start = 0;
       let length = 1;
       for (let match of pattern.allMatches(this)) {
-        let matchStart = dart.as(dart.dload(match, 'start'), core.int);
-        let matchEnd = dart.as(dart.dload(match, 'end'), core.int);
+        let matchStart = match.start;
+        let matchEnd = match.end;
         length = dart.notNull(matchEnd) - dart.notNull(matchStart);
         if (length === 0 && start === matchStart) {
           continue;