Remove BindStateHolder and have Bind() return a Callback<> object directly.

base/bind.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
 $$ can be found here:
 $$
 $$ http://code.google.com/p/googletest/wiki/PumpManual
 $$
 
 $$
 $$ MAX_ARITY controls the number of arguments that Bind() supports.
 $$ The amount of code, and more importantly, the number of template types
@@ skipping 53 matching lines @@
 // harder to read.
 
 namespace base {
 
 $range ARITY 0..MAX_ARITY
 $for ARITY [[
 $range ARG 1..ARITY
 
 template <typename Functor[[]]
 $if ARITY > 0 [[, ]] $for ARG , [[typename P$(ARG)]]>
-internal::BindStateHolder<
-    internal::BindState<
+base::Callback<
+    typename internal::BindState<
         typename internal::FunctorTraits<Functor>::RunnableType,
         typename internal::FunctorTraits<Functor>::RunType,
-        void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])> >
+        void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])>
+            ::UnboundRunType>
 Bind(Functor functor
 $if ARITY > 0 [[, ]] $for ARG , [[const P$(ARG)& p$(ARG)]]) {
   // Typedefs for how to store and run the functor.
   typedef typename internal::FunctorTraits<Functor>::RunnableType RunnableType;
   typedef typename internal::FunctorTraits<Functor>::RunType RunType;
 
   // Use RunnableType::RunType instead of RunType above because our
   // checks should below for bound references need to know what the actual
   // functor is going to interpret the argument as.
   typedef internal::FunctionTraits<typename RunnableType::RunType>
@@ skipping 29 matching lines @@
   COMPILE_ASSERT(!internal::HasIsMethodTag<RunnableType>::value ||
                      !is_array<P$(ARG)>::value,
                  first_bound_argument_to_method_cannot_be_array);
 ]] $else [[
   COMPILE_ASSERT(!internal::NeedsScopedRefptrButGetsRawPtr<P$(ARG)>::value,
                  p$(ARG)_is_refcounted_type_and_needs_scoped_refptr);
 ]]  $$ $if ARG
 
 ]]  $$ $for ARG
 
+  typedef internal::BindState<RunnableType, RunType, [[]]
+void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])> [[]]
+BindState;
 
-  return internal::MakeBindStateHolder(
-      new internal::BindState<RunnableType, RunType, [[]]
-void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])>(
-          internal::MakeRunnable(functor)[[]]
+
+  return Callback<typename BindState::UnboundRunType>(
+      new BindState(internal::MakeRunnable(functor)[[]]
 $if ARITY > 0 [[, ]] $for ARG , [[p$(ARG)]]));
 }
 
 ]]  $$ for ARITY
 
 }  // namespace base
 
 #endif  // BASE_BIND_H_