Support type variables on redirecting factory constructors.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/elements.dart b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
index bd1fac27c4711b46bd10e9ba0ecdd2e11f758774..3d7982b191f17fd7909a0e599a38c726e250ab87 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -721,6 +721,8 @@ abstract class FunctionSignature {
   void forEachOptionalParameter(void function(Element parameter));
 
   void orderedForEachParameter(void function(Element parameter));
+
+  bool isCompatibleWith(FunctionSignature constructorSignature);
 }
 
 abstract class FunctionElement extends Element {
@@ -733,6 +735,8 @@ abstract class FunctionElement extends Element {
   FunctionElement get patch;
   FunctionElement get origin;
 
+  bool get isRedirectingFactory;
+
   // TODO(kasperl): These are bit fishy. Do we really need them?
   void set patch(FunctionElement value);
   void set origin(FunctionElement value);