dart2js: Don't zone-register callbacks in async functions for every await.

pkg/compiler/lib/src/elements/modelx.dart

Index: pkg/compiler/lib/src/elements/modelx.dart
diff --git a/pkg/compiler/lib/src/elements/modelx.dart b/pkg/compiler/lib/src/elements/modelx.dart
index ee7936efc2cb7dd0790f2a01bc886377ea0a9ed4..48aed6ddcb7ce1e49fdb56d6f0225c81709f5131 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -1003,10 +1003,12 @@ class LibraryElementX
   /** Look up a top-level element in this library, but only look for
     * non-imported elements. Returns null if no such element exist. */
   Element findLocal(String elementName) {
-    // TODO(johnniwinther): How to handle injected elements in the patch
+    // TODO((johnniwinther): How to handle injected elements in the patch
     // library?
     Element result = localScope.lookup(elementName);
-    if (result == null || result.library != this) return null;
+    if (result == null && isPatch) {
+      return origin.findLocal(elementName);
+    }
     return result;
   }