Callback API Change: Allow Bind() to take a Callback<> and bind all its free parameters.

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
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 $var MAX_ARITY = 6
 
 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
@@ skipping 45 matching lines @@
 internal::InvokerStorageHolder<internal::InvokerStorage$(BOUND)<Sig,
 $for BOUND_ARG , [[P$(BOUND_ARG)]]> >
 Bind(Sig f, $for BOUND_ARG , [[const P$(BOUND_ARG)& p$(BOUND_ARG)]]) {
   return internal::MakeInvokerStorageHolder(
       new internal::InvokerStorage$(BOUND)<Sig, [[]]
 $for BOUND_ARG , [[P$(BOUND_ARG)]]>(
           f, $for BOUND_ARG , [[p$(BOUND_ARG)]]));
 }
 
 ]]
+]]  $$ for BOUND
+
+// Specializations to allow binding all the free arguments in a
+// pre-existing base::Callback<>. This does not give full support for
+// currying, but is significantly simpler and addresses the use case
+// where a base::Callback<> needs to be invoked on another context/thread.
+$for BOUND [[
+$range BOUND_ARG 1..BOUND
+$if BOUND != 0 [[
+
+template <typename Sig, $for BOUND_ARG , [[typename P$(BOUND_ARG)]]>
+base::Closure Bind(const base::Callback<Sig>& callback, [[]]
+$for BOUND_ARG , [[const P$(BOUND_ARG)& p$(BOUND_ARG)]]) {
+  return base::Bind([[]]
+&internal::BindMoreFunc$(BOUND)<Sig, $for BOUND_ARG , [[P$(BOUND_ARG)]]>, [[]]
+callback, [[]]
+$for BOUND_ARG , [[p$(BOUND_ARG)]]);
+}
+
+]]
 
 ]]  $$ for BOUND
 
 }  // namespace base
 
 #endif  // BASE_BIND_H_