Fix typechecks for constant assignments of function to typedefs.

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

Index: sdk/lib/_internal/compiler/implementation/constants.dart
diff --git a/sdk/lib/_internal/compiler/implementation/constants.dart b/sdk/lib/_internal/compiler/implementation/constants.dart
index 272fd6a5cd201f82c7fd1eec4ceaa17e7bb834a8..b5f7a1a6ac5bbb3a1c2870d638d204cf44e9b3d0 100644
--- a/sdk/lib/_internal/compiler/implementation/constants.dart
+++ b/sdk/lib/_internal/compiler/implementation/constants.dart
@@ -75,9 +75,8 @@ class FunctionConstant extends Constant {
     return new DartString.literal(element.name);
   }
 
-  DartType computeType(Compiler compiler) {
-    return compiler.functionClass.computeType(compiler);
-  }
+  // TODO(johnniwinther): remove computeType.
+  DartType computeType(Compiler compiler) => element.computeType(compiler);
 
   ti.TypeMask computeMask(Compiler compiler) {
     return compiler.typesTask.functionType;