Add support for fields to the new dart backend.

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

Index: pkg/compiler/lib/src/cps_ir/redundant_phi.dart
diff --git a/pkg/compiler/lib/src/cps_ir/redundant_phi.dart b/pkg/compiler/lib/src/cps_ir/redundant_phi.dart
index 11c6bf088639f5cec3a10c03f617c2b38ce994ac..dbf3686c8e69ead9bd3175358b39254a602e91bc 100644
--- a/pkg/compiler/lib/src/cps_ir/redundant_phi.dart
+++ b/pkg/compiler/lib/src/cps_ir/redundant_phi.dart
@@ -15,8 +15,18 @@ part of dart2js.optimizers;
 class RedundantPhiEliminator extends RecursiveVisitor implements Pass {
   final Set<Continuation> workSet = new Set<Continuation>();
 
-  void rewrite(final FunctionDefinition root) {
+  void rewrite(final ExecutableDefinition root) => root.acceptPass(this);
+
+  void rewriteFunctionDefinition(final FunctionDefinition root) {
     if (root.isAbstract) return;
+    rewriteExecutableDefinition(root);
+  }
+
+  void rewriteFieldDefinition(final FieldDefinition root) {
+    rewriteExecutableDefinition(root);
+  }
+
+  void rewriteExecutableDefinition(final ExecutableDefinition root) {
 
     // Set all parent pointers.
     new _ParentVisitor().visit(root);