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

base/callback_internal.cc

Index: base/callback_internal.cc
diff --git a/base/callback_internal.cc b/base/callback_internal.cc
index 582fbdc12c43b520f81e5684c3dde02072e476ea..abfdc736a1bc870a9b84256bb32c209518635679 100644
--- a/base/callback_internal.cc
+++ b/base/callback_internal.cc
@@ -21,12 +21,9 @@ bool CallbackBase::Equals(const CallbackBase& other) const {
          polymorphic_invoke_ == other.polymorphic_invoke_;
 }
 
-CallbackBase::CallbackBase(InvokeFuncStorage polymorphic_invoke,
-                           scoped_refptr<BindStateBase>* bind_state)
-    : polymorphic_invoke_(polymorphic_invoke) {
-  if (bind_state) {
-    bind_state_.swap(*bind_state);
-  }
+CallbackBase::CallbackBase(BindStateBase* bind_state)
+    : bind_state_(bind_state),

[akalin, 2011/12/02 18:54:45]

This constructor should only be called with a newly-constructed bind state,
right?  Can we assert that that is so, i.e. check that bind_state->HasOneRef()
is false before we set bind_state_ to it?

[awong, 2011/12/06 00:21:12]

Added a DCHECK, though it feels slightly overkill since no one should be new-ing
a base::internal struct...

+      polymorphic_invoke_(NULL) {
 }
 
 CallbackBase::~CallbackBase() {