dart2js: switching isolate is not 'PURE'

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 438dbe6d1797ecdcef10d0ae306075f3c9bfdcab..2ac21b970668342aa08df07f4b602dad62a1bb70 100644
--- a/pkg/compiler/lib/src/native/behavior.dart
+++ b/pkg/compiler/lib/src/native/behavior.dart
@@ -111,6 +111,9 @@ class NativeBehavior {
   static NativeBehavior get PURE => NativeBehavior._makePure();
   static NativeBehavior get PURE_ALLOCATION =>
       NativeBehavior._makePure(isAllocation: true);
+  static NativeBehavior get CHANGES_STATIC_PROPERTY =>
+      NativeBehavior._makeAssignsStaticProperty();
+
 
   String toString() {
     return 'NativeBehavior('
@@ -132,6 +135,16 @@ class NativeBehavior {
     return behavior;
   }
 
+  static NativeBehavior _makeAssignsStaticProperty() {
+    NativeBehavior behavior = new NativeBehavior();
+    behavior.sideEffects.clearAllDependencies();
+    behavior.sideEffects.clearAllSideEffects();
+    behavior.sideEffects.setChangesStaticProperty();
+    behavior.throwBehavior = NativeThrowBehavior.NEVER;
+    behavior.isAllocation = false;
+    return behavior;
+  }
+
   /// Processes the type specification string of a call to JS and stores the
   /// result in the [typesReturned] and [typesInstantiated]. It furthermore
   /// computes the side effects, and, if given, invokes [setSideEffects] with