dart2js cps: Refactor tracking of side effects.

pkg/compiler/lib/src/cps_ir/builtin_operator.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library builtin_operator;
 // This is shared by the CPS and Tree IRs.
 // Both cps_ir_nodes and tree_ir_nodes import and re-export this file.
 
+import 'effects.dart';
+
 /// An operator supported natively in the CPS and Tree IRs using the
 /// `ApplyBuiltinOperator` instructions.
 ///
 /// These operators are pure in the sense that they cannot throw, diverge,
 /// have observable side-effects, return new objects, nor depend on any
 /// mutable state.
 ///
 /// Most operators place restrictions on the values that may be given as
 /// argument; their behaviour is unspecified if those requirements are violated.
 ///
@@ skipping 171 matching lines @@
     case BuiltinOperator.NumSubtract:
     case BuiltinOperator.NumMultiply:
     case BuiltinOperator.NumDivide:
     case BuiltinOperator.NumRemainder:
     case BuiltinOperator.StringConcatenate:
       return true;
     default:
       return false;
   }
 }
+
+int getEffectsOfBuiltinMethod(BuiltinMethod method) {
+  switch (method) {
+    case BuiltinMethod.Push:
+      return Effects.changesIndexableContent | Effects.changesIndexableLength;
+    case BuiltinMethod.Pop:
+      return Effects.dependsOnIndexableContent | Effects.changesIndexableLength;
+  }
+}