[mojo] Use base::Pickle for Message storage.

mojo/public/cpp/bindings/lib/pickle_buffer.cc

+// 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.
+
+#include "mojo/public/cpp/bindings/lib/pickle_buffer.h"
+
+#include <stdlib.h>
+
+#include "base/logging.h"
+#include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
+
+namespace mojo {
+namespace internal {
+
+PickleBuffer::PickleBuffer() : base::Pickle(sizeof(PaddedHeader)) {
+  headerT<PaddedHeader>()->padding = 0;
+}
+
+PickleBuffer::~PickleBuffer() {
+}
+
+void PickleBuffer::AllocData(uint32_t num_bytes) {
+  AllocUninitializedData(num_bytes);
+  memset(data(), 0, num_bytes);
+}
+
+void PickleBuffer::AllocUninitializedData(uint32_t num_bytes) {
+  // Data should only ever be explicitly allocated through AllocData or
+  // AllocUninitializedData if the buffer has no existing data in it yet.
+  DCHECK(payload_size() == 0);
+  Resize(num_bytes);
+}
+
+void* PickleBuffer::Allocate(size_t num_bytes) {
+  // The last allocation may terminate in between 8-byte boundaries. Pad the
+  // front of this allocation if that's the case.
+  size_t padding_bytes = (8 - (payload_size() % 8)) % 8;
+  size_t previous_capacity = capacity_after_header();
+  char* p = reinterpret_cast<char*>(ClaimBytes(padding_bytes + num_bytes));
+  DCHECK_EQ(capacity_after_header(), previous_capacity)
+      << "Message buffers must be fully allocated before serialization.";
+  return p + padding_bytes;
+}
+
+PickleBuffer* PickleBuffer::AsPickleBuffer() { return this; }
+
+}  // namespace internal
+}  // namespace mojo