dart2js cps: Support sync* and yield.

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
index 3390b8ca281e18287b6cbb9e479e06c7a462afa3..ca34d15f0107b02e2801c7f76694381a6ef593f1 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
@@ -2806,8 +2806,13 @@ class IrBuilder {
   ir.Node buildAwait(ir.Primitive value) {
     return _continueWithExpression((k) => new ir.Await(value, k));
   }
-}
 
+  void buildYield(ir.Primitive value, bool hasStar) {
+    _continueWithExpression((k) {
+      return new ir.Yield(value, hasStar, k);
+    });
+  }
+}
 
 /// Location of a variable relative to a given closure.
 class ClosureLocation {