[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::ReserveCapacity(uint32_t num_bytes) {
+  ReserveUninitializedCapacity(num_bytes);
+  memset(data(), 0, num_bytes);
+}
+
+void PickleBuffer::ReserveUninitializedCapacity(uint32_t num_bytes) {
+  // Data should only ever be explicitly allocated through ReserveCapacity or
+  // ReserveUninitializedCapacity 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 padded_capacity = Align(payload_size());
+  DCHECK_GE(padded_capacity, payload_size());
+  size_t padding_bytes = padded_capacity - payload_size();
+  size_t available_capacity = capacity_after_header() - payload_size();
+  size_t allocation_size = padding_bytes + num_bytes;
+  const void* previous_data_location = data();
+  if (available_capacity < allocation_size) {
+    NOTREACHED() <<
+        "Message buffers must be fully allocated before serialization.";
+    return nullptr;
+  }
+  char* p = reinterpret_cast<char*>(ClaimBytes(allocation_size));
+  DCHECK_EQ(data(), previous_data_location);
+  return p + padding_bytes;
+}
+
+PickleBuffer* PickleBuffer::AsPickleBuffer() { return this; }
+
+}  // namespace internal
+}  // namespace mojo