Add CdmWrapper to support multiple CDM versions in CdmAdapter.

media/cdm/ppapi/linked_ptr.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This is a copy of base/linked_ptr.h with CHECKS/DCHECKS replaced with
 // PP_DCHECKs.
 //
 // A "smart" pointer type with reference tracking.  Every pointer to a
 // particular object is kept on a circular linked list.  When the last pointer
 // to an object is destroyed or reassigned, the object is deleted.
@@ skipping 97 matching lines @@
     }
     return *this;
   }
 
   // Smart pointer members.
   void reset(T* ptr = NULL) {
     depart();
     capture(ptr);
   }
   T* get() const { return value_; }
+  operator T*() const { return value_; }

[ddorwin, 2013/10/18 22:17:01]

You probably don't need this based on my comments. Also, I think it's better to
avoid modifying this in ways that base/ does not have, especially if the impact
is just a few more characters in a small number of places.

[xhwang, 2013/10/18 23:03:52]

It's used in a lot of places in CdmAdapter. So I'd like to keep this change.
WDYT?

[ddorwin, 2013/10/18 23:45:56]

As discussed, this is fine.

   T* operator->() const { return value_; }
   T& operator*() const { return *value_; }
   // Release ownership of the pointed object and returns it.
   // Sole ownership by this linked_ptr object is required.
   T* release() {
     bool last = link_.depart();
     PP_DCHECK(last);
     (void)last;
     T* v = value_;
     value_ = NULL;
@@ skipping 48 matching lines @@
 
 // A function to convert T* into linked_ptr<T>
 // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
 // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
 template <typename T>
 linked_ptr<T> make_linked_ptr(T* ptr) {
   return linked_ptr<T>(ptr);
 }
 
 #endif  // MEDIA_CDM_PPAPI_LINKED_PTR_H_