Split TypedSelector into Selector and TypeMask.

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 027a3d67a972c19c2f67004f01160ababc442565..05690c2e9be5eb8d1284594fbe0a9e5fdb5f81b8 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -51,8 +51,8 @@ class TypeMaskSystem {
     return inferrer.getGuaranteedReturnTypeOfElement(function);
   }
 
-  TypeMask getSelectorReturnType(Selector selector) {
-    return inferrer.getGuaranteedTypeOfSelector(selector);
+  TypeMask getSelectorReturnType(Selector selector, TypeMask mask) {
+    return inferrer.getGuaranteedTypeOfSelector(selector, mask);
   }
 
   TypeMask getFieldType(FieldElement field) {
@@ -729,7 +729,8 @@ class TypePropagationVisitor implements Visitor {
     }
     if (!node.selector.isOperator) {
       // TODO(jgruber): Handle known methods on constants such as String.length.
-      setResult(nonConstant(typeSystem.getSelectorReturnType(node.selector)));
+      setResult(nonConstant(
+          typeSystem.getSelectorReturnType(node.selector, node.mask)));
       return;
     }