dart2js cps: Support sync* and yield.

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

Index: pkg/compiler/lib/src/cps_ir/type_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_propagation.dart b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
index e3db1e324637a7c0e6af2ec283aad290f5a67ef7..a99a7ab68e6618f56211e6bd416df6451b28a66c 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -2117,7 +2117,7 @@ class TypePropagationVisitor implements Visitor {
   }
 
   void visitInvokeStatic(InvokeStatic node) {
-    if (node.target.library.isInternalLibrary) {
+    if (node.target.library != null && node.target.library.isInternalLibrary) {
       switch (node.target.name) {
         case InternalMethod.Stringify:
           AbstractValue argValue = getValue(node.arguments[0].definition);
@@ -2522,6 +2522,11 @@ class TypePropagationVisitor implements Visitor {
   }
 
   @override
+  visitYield(Yield node) {
+    setReachable(node.continuation.definition);
+  }
+
+  @override
   void visitRefinement(Refinement node) {
     AbstractValue value = getValue(node.value.definition);
     if (value.isNothing ||