Allow copying scoped_nsobject of different type.

base/mac/scoped_nsobject.h

Index: base/mac/scoped_nsobject.h
diff --git a/base/mac/scoped_nsobject.h b/base/mac/scoped_nsobject.h
index 8d7bd4a27bd37c2844704e8beb2f0ef3bb849469..8814b51439b6f76e96e3e235bb620438009cdc50 100644
--- a/base/mac/scoped_nsobject.h
+++ b/base/mac/scoped_nsobject.h
@@ -40,6 +40,11 @@ class scoped_nsprotocol {
       : object_([that.object_ retain]) {
   }
 
+  template <typename NSU>
+  scoped_nsprotocol(const scoped_nsprotocol<NSU>& that)
+      : object_([that.get() retain]) {
+  }
+
   ~scoped_nsprotocol() {
     [object_ release];
   }
@@ -119,6 +124,11 @@ class scoped_nsobject : public scoped_nsprotocol<NST*> {
       : scoped_nsprotocol<NST*>(that) {
   }
 
+  template<typename NSU>
+  scoped_nsobject(const scoped_nsobject<NSU>& that)
+      : scoped_nsprotocol<NST*>(that) {
+  }
+
   scoped_nsobject& operator=(const scoped_nsobject<NST>& that) {
     scoped_nsprotocol<NST*>::operator=(that);
     return *this;
@@ -135,6 +145,11 @@ class scoped_nsobject<id> : public scoped_nsprotocol<id> {
       : scoped_nsprotocol<id>(that) {
   }
 
+  template<typename NSU>
+  scoped_nsobject(const scoped_nsobject<NSU>& that)
+      : scoped_nsprotocol<id>(that) {
+  }
+
   scoped_nsobject& operator=(const scoped_nsobject<id>& that) {
     scoped_nsprotocol<id>::operator=(that);
     return *this;