Support typedefs in function signatures.

sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
index eb1fdaea4682927cac22d8f902cbe60d527b69ee..568dfc8cbf978b2bd29f27a66bbf36dad60445c9 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
@@ -822,6 +822,7 @@ class Namer implements ClosureNamer {
         // other elements, such as bound closures also live in [currentIsolate].
         !element.isAccessor &&
         !element.isClass &&
+        !element.isTypedef &&
         !element.isConstructor &&
         !element.isFunction &&
         !element.isLibrary;
@@ -883,6 +884,8 @@ class Namer implements ClosureNamer {
 
   String operatorSignature() => r'$signature';
 
+  String typedefTag() => r'typedef';
+
   String functionTypeTag() => r'func';
 
   String functionTypeVoidReturnTag() => r'void';