Out of line CallbackBase's copy and assignment operators.

base/callback_internal.h

Index: base/callback_internal.h
diff --git a/base/callback_internal.h b/base/callback_internal.h
index 9dca02387dcef60e7afadf31fc232dadf1069a28..8a5c4378bc1ccbfb5303727ecfd129dc49a42903 100644
--- a/base/callback_internal.h
+++ b/base/callback_internal.h
@@ -36,6 +36,9 @@ class BindStateBase : public RefCountedThreadSafe<BindStateBase> {
 // template bloat.
 class BASE_EXPORT CallbackBase {
  public:
+  CallbackBase(const CallbackBase& c);
+  CallbackBase& operator=(const CallbackBase& c);
+
   // Returns true if Callback is null (doesn't refer to anything).
   bool is_null() const { return bind_state_.get() == NULL; }