Make Callback.Equals() only work when comparing against the same type.

base/callback.h

Index: base/callback.h
diff --git a/base/callback.h b/base/callback.h
index c1f584d52f535450bfc003b3152a01ca01545510..03abb4bf71d58b8683befaca07f91daa525e4b52 100644
--- a/base/callback.h
+++ b/base/callback.h
@@ -258,6 +258,10 @@ class Callback<R(void)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run() const {
     PolymorphicInvoke f =
         reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
@@ -292,6 +296,10 @@ class Callback<R(A1)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run(typename internal::ParamTraits<A1>::ForwardType a1) const {
     PolymorphicInvoke f =
         reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
@@ -327,6 +335,10 @@ class Callback<R(A1, A2)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run(typename internal::ParamTraits<A1>::ForwardType a1,
         typename internal::ParamTraits<A2>::ForwardType a2) const {
     PolymorphicInvoke f =
@@ -365,6 +377,10 @@ class Callback<R(A1, A2, A3)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run(typename internal::ParamTraits<A1>::ForwardType a1,
         typename internal::ParamTraits<A2>::ForwardType a2,
         typename internal::ParamTraits<A3>::ForwardType a3) const {
@@ -406,6 +422,10 @@ class Callback<R(A1, A2, A3, A4)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run(typename internal::ParamTraits<A1>::ForwardType a1,
         typename internal::ParamTraits<A2>::ForwardType a2,
         typename internal::ParamTraits<A3>::ForwardType a3,
@@ -451,6 +471,10 @@ class Callback<R(A1, A2, A3, A4, A5)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run(typename internal::ParamTraits<A1>::ForwardType a1,
         typename internal::ParamTraits<A2>::ForwardType a2,
         typename internal::ParamTraits<A3>::ForwardType a3,
@@ -499,6 +523,10 @@ class Callback<R(A1, A2, A3, A4, A5, A6)> : public internal::CallbackBase {
                    callback_type_does_not_match_bind_result);
   }
 
+  bool Equals(const Callback& other) const {
+    return CallbackBase::Equals(other);
+  }
+
   R Run(typename internal::ParamTraits<A1>::ForwardType a1,
         typename internal::ParamTraits<A2>::ForwardType a2,
         typename internal::ParamTraits<A3>::ForwardType a3,