Sync MDP: implement MemoryDumpProvider

components/sync/base/proto_value_ptr.h

 // Copyright 2015 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.
 
 #ifndef COMPONENTS_SYNC_BASE_PROTO_VALUE_PTR_H_
 #define COMPONENTS_SYNC_BASE_PROTO_VALUE_PTR_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
 
@@ skipping 71 matching lines @@
 
   const T& value() const {
     return wrapper_ ? wrapper_->value() : Traits::DefaultValue();
   }
 
   const T* operator->() const {
     const T& wrapped_instance = value();
     return &wrapped_instance;
   }
 
+  explicit operator bool () const { return wrapper_ != nullptr; }
+  bool operator == (decltype(nullptr)) const { return wrapper_ == nullptr; }
+  bool operator != (decltype(nullptr)) const { return wrapper_ != nullptr; }
+
  private:
   friend struct syncable::EntryKernel;
   friend struct syncer_v2::EntityData;
   friend class syncer_v2::ProcessorEntityTracker;
   FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, ValueAssignment);
   FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, ValueSwap);
   FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, SharingTest);
   FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, ParsingTest);
 
   // set the value to copy of |new_value|.
@@ skipping 18 matching lines @@
     }
   }
 
   void load(const void* blob, int length) {
     wrapper_ = Wrapper::ParseFromBlob(blob, length);
   }
 
   scoped_refptr<Wrapper> wrapper_;
 };
 
+template <typename T, typename Traits>
+size_t EstimateMemoryUsage(const ProtoValuePtr<T, Traits>& ptr) {
+  return ptr? EstimateMemoryUsage(ptr.value()) : 0;
+}
+
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_BASE_PROTO_VALUE_PTR_H_