Add support for fields to the new dart backend.

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

Index: pkg/compiler/lib/src/cps_ir/constant_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/constant_propagation.dart b/pkg/compiler/lib/src/cps_ir/constant_propagation.dart
index fcf5c1b8bb482cf7e31a748ef1afb5b0aba3b3a2..a6da66be1402f03f61a67e6027f9931f3c076170 100644
--- a/pkg/compiler/lib/src/cps_ir/constant_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/constant_propagation.dart
@@ -12,7 +12,7 @@ part of dart2js.optimizers;
  * Implemented according to 'Constant Propagation with Conditional Branches'
  * by Wegman, Zadeck.
  */
-class ConstantPropagator implements Pass {
+class ConstantPropagator extends Pass {
 
   // Required for type determination in analysis of TypeOperator expressions.
   final dart2js.Compiler _compiler;
@@ -23,11 +23,8 @@ class ConstantPropagator implements Pass {
 
   ConstantPropagator(this._compiler, this._constantSystem);
 
-  void rewrite(FunctionDefinition root) {
-    if (root.isAbstract) return;
-
+  void _rewriteExecutableDefinition(ExecutableDefinition root) {
     // Set all parent pointers.
-
     new ParentVisitor().visit(root);
 
     // Analyze. In this phase, the entire term is analyzed for reachability
@@ -45,6 +42,16 @@ class ConstantPropagator implements Pass {
         analyzer.reachableNodes, analyzer.node2value);
     transformer.transform(root);
   }
+
+  void rewriteFunctionDefinition(FunctionDefinition root) {
+    if (root.isAbstract) return;
+    _rewriteExecutableDefinition(root);
+  }
+
+  void rewriteFieldDefinition(FieldDefinition root) {
+    _rewriteExecutableDefinition(root);
+  }
+
 }
 
 /**
@@ -58,8 +65,8 @@ class _TransformingVisitor extends RecursiveVisitor {
 
   _TransformingVisitor(this.reachable, this.node2value);
 
-  void transform(FunctionDefinition root) {
-    visitFunctionDefinition(root);
+  void transform(ExecutableDefinition root) {
+    visit(root);
   }
 
   /// Given an expression with a known constant result and a continuation,
@@ -226,7 +233,7 @@ class _ConstPropagationVisitor extends Visitor {
 
   _ConstPropagationVisitor(this.compiler, this.constantSystem);
 
-  void analyze(FunctionDefinition root) {
+  void analyze(ExecutableDefinition root) {
     reachableNodes.clear();
     defWorkset.clear();
     nodeWorklist.clear();
@@ -304,6 +311,10 @@ class _ConstPropagationVisitor extends Visitor {
     setReachable(node.body);
   }
 
+  void visitFieldDefinition(FieldDefinition node) {
+    setReachable(node.body);
+  }
+
   // Expressions.
 
   void visitLetPrim(LetPrim node) {