[Sync] Move //sync to //components/sync.

sync/internal_api/public/util/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 SYNC_INTERNAL_API_PUBLIC_UTIL_PROTO_VALUE_PTR_H_
-#define SYNC_INTERNAL_API_PUBLIC_UTIL_PROTO_VALUE_PTR_H_
-
-#include "base/gtest_prod_util.h"
-#include "base/memory/ref_counted.h"
-
-namespace syncer_v2 {
-struct EntityData;
-class ProcessorEntityTracker;
-}  // namespace syncer_v2
-
-namespace syncer {
-
-namespace syncable {
-struct EntryKernel;
-}  // namespace syncable
-
-// Default traits struct for ProtoValuePtr - adapts a
-// ::google::protobuf::MessageLite derived type to be used with ProtoValuePtr.
-template <typename T>
-struct DefaultProtoValuePtrTraits {
-  // Deep copy the value from |src| to |dest|.
-  static void CopyValue(T* dest, const T& src) { dest->CopyFrom(src); }
-  // Swap the value with the source (to avoid deep copying).
-  static void SwapValue(T* dest, T* src) { dest->Swap(src); }
-  // Parse the value from BLOB.
-  static void ParseFromBlob(T* dest, const void* blob, int length) {
-    dest->ParseFromArray(blob, length);
-  }
-  // True if the |value| is a non-default value.
-  static bool HasValue(const T& value) { return value.ByteSize() > 0; }
-  // Default value for the type.
-  static const T& DefaultValue() { return T::default_instance(); }
-};
-
-// This is a smart pointer to a ::google::protobuf::MessageLite derived type
-// that implements immutable, shareable, copy-on-write semantics.
-//
-// Additionally this class helps to avoid storing multiple copies of default
-// instances of the wrapped type.
-//
-// Copying ProtoValuePtr results in ref-counted sharing of the
-// underlying wrapper and the value contained in the wrapper.
-//
-// The public interface includes only immutable access to the wrapped value.
-// The only way to assign a value to ProtoValuePtr is through a
-// private SetValue function which is called from EntryKernel. That results
-// in stopping sharing the previous value and creating a wrapper to the new
-// value.
-template <typename T, typename Traits = DefaultProtoValuePtrTraits<T>>
-class ProtoValuePtr {
- private:
-  // Immutable shareable ref-counted wrapper that embeds the value.
-  class Wrapper : public base::RefCountedThreadSafe<Wrapper> {
-   public:
-    explicit Wrapper(const T& value) { Traits::CopyValue(&value_, value); }
-    explicit Wrapper(T* value) { Traits::SwapValue(&value_, value); }
-
-    const T& value() const { return value_; }
-    // Create wrapper by deserializing a BLOB.
-    static Wrapper* ParseFromBlob(const void* blob, int length) {
-      Wrapper* wrapper = new Wrapper;
-      Traits::ParseFromBlob(&wrapper->value_, blob, length);
-      return wrapper;
-    }
-
-   private:
-    friend class base::RefCountedThreadSafe<Wrapper>;
-    Wrapper() {}
-    ~Wrapper() {}
-
-    T value_;
-  };
-
- public:
-  ProtoValuePtr() {}
-  ~ProtoValuePtr() {}
-
-  const T& value() const {
-    return wrapper_ ? wrapper_->value() : Traits::DefaultValue();
-  }
-
-  const T* operator->() const {
-    const T& wrapped_instance = value();
-    return &wrapped_instance;
-  }
-
- 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|.
-  void set_value(const T& new_value) {
-    if (Traits::HasValue(new_value)) {
-      wrapper_ = new Wrapper(new_value);
-    } else {
-      // Don't store default value.
-      reset();
-    }
-  }
-
-  void reset() { wrapper_ = nullptr; }
-
-  // Take over |src| value (swap).
-  void swap_value(T* src) {
-    if (Traits::HasValue(*src)) {
-      wrapper_ = new Wrapper(src);
-    } else {
-      // Don't store default value.
-      reset();
-    }
-  }
-
-  void load(const void* blob, int length) {
-    wrapper_ = Wrapper::ParseFromBlob(blob, length);
-  }
-
-  scoped_refptr<Wrapper> wrapper_;
-};
-
-}  // namespace syncer
-
-#endif  // SYNC_INTERNAL_API_PUBLIC_UTIL_PROTO_VALUE_PTR_H_