dart2js cps: Better GVN for fixed lengths and unmodified fields.

pkg/compiler/lib/src/js_backend/codegen/task.dart

Index: pkg/compiler/lib/src/js_backend/codegen/task.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/task.dart b/pkg/compiler/lib/src/js_backend/codegen/task.dart
index cad67af3c8e528e146e92a00d64e309e8dd32a70..36972b6675613d02555eb8cb760b4f93fa17bb19 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/task.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/task.dart
@@ -208,7 +208,7 @@ class CpsFunctionCompiler implements FunctionCompiler {
       applyCpsPass(new RedundantJoinEliminator(), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
       applyCpsPass(new RedundantRefinementEliminator(typeSystem), cpsFunction);
-      applyCpsPass(new GVN(compiler), cpsFunction);
+      applyCpsPass(new GVN(compiler, typeSystem), cpsFunction);
       applyCpsPass(new RemoveRefinements(), cpsFunction);
       applyCpsPass(new ShrinkingReducer(), cpsFunction);
       applyCpsPass(new ScalarReplacer(compiler), cpsFunction);