Support type variables on redirecting factory constructors.

sdk/lib/_internal/compiler/implementation/tree/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/tree/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/tree/nodes.dart b/sdk/lib/_internal/compiler/implementation/tree/nodes.dart
index a2216cdcf74f49576586ca6eb03e0c873807e5a1..9a3c43cd1ea3901620f790b941416f36be69ce01 100644
--- a/sdk/lib/_internal/compiler/implementation/tree/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/tree/nodes.dart
@@ -702,6 +702,11 @@ class FunctionExpression extends Expression {
 
   accept(Visitor visitor) => visitor.visitFunctionExpression(this);
 
+  bool get isRedirectingFactory {
+    return body != null && body.asReturn() != null &&
+        body.asReturn().isRedirectingFactoryBody;
+  }
+
   visitChildren(Visitor visitor) {
     if (modifiers != null) modifiers.accept(visitor);
     if (returnType != null) returnType.accept(visitor);