Remove signature classes from the VM.

runtime/vm/bootstrap.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap.h"
 
 #include "include/dart_api.h"
 
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
@@ skipping 321 matching lines @@
                              bootstrap_libraries[i].patch_paths_);
       if (!error.IsNull()) {
         break;
       }
     }
   }
   if (error.IsNull()) {
     SetupNativeResolver();
     ClassFinalizer::ProcessPendingClasses();
 
-    Class& cls = Class::Handle(zone);
-    // Eagerly compile the function implementation class as it is the super
-    // class of signature classes. This allows us to just finalize signature
-    // classes without going through the hoops of trying to compile them.
-    const Type& type =
-        Type::Handle(zone, isolate->object_store()->function_impl_type());
-    cls = type.type_class();
+    // Eagerly compile the _Closure class as it is the class of all closure
+    // instances. This allows us to just finalize function types
+    // without going through the hoops of trying to compile their scope class.
+    const Class& cls =
+        Class::Handle(zone, isolate->object_store()->closure_class());
     Compiler::CompileClass(cls);
   }
 
   // Restore the library tag handler for the isolate.
   isolate->set_library_tag_handler(saved_tag_handler);
 
   return error.raw();
 }
 
 }  // namespace dart