dart2js cps: Refactor tracking of side effects.

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

Index: pkg/compiler/lib/src/cps_ir/builtin_operator.dart
diff --git a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
index 2db4ac5bf62d70ee7a348e735609df5152f1abfd..48e8851b950b84d4591a38b3670bbf43032b19d8 100644
--- a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
+++ b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
@@ -5,6 +5,8 @@ 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.
 ///
@@ -196,3 +198,12 @@ bool isCompoundableOperator(BuiltinOperator operator) {
       return false;
   }
 }
+
+int getEffectsOfBuiltinMethod(BuiltinMethod method) {
+  switch (method) {
+    case BuiltinMethod.Push:
+      return Effects.changesIndexableContent | Effects.changesIndexableLength;
+    case BuiltinMethod.Pop:
+      return Effects.dependsOnIndexableContent | Effects.changesIndexableLength;
+  }
+}