Implements JS bindings for mojo shared buffer.

third_party/WebKit/Source/core/mojo/MojoSharedBufferMapping.cpp

+// Copyright 2017 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 "core/mojo/MojoSharedBufferMapping.h"
+
+#include "core/dom/DOMArrayBuffer.h"
+#include "mojo/public/cpp/system/core.h"
+
+namespace blink {
+
+MojoSharedBufferMapping::MojoSharedBufferMapping(void* data, unsigned numBytes)
+    : m_buffer(DOMArrayBuffer::create(data, numBytes)) {
+  // TODO(alokp): We need to create an ArrayBuffer that does not own data.
+}
+
+MojoSharedBufferMapping::~MojoSharedBufferMapping() {
+  unmap();
+}
+
+void MojoSharedBufferMapping::unmap() {
+  if (!m_buffer)
+    return;
+
+  MojoResult result = MojoUnmapBuffer(m_buffer->data());
+  DCHECK_EQ(MOJO_RESULT_OK, result);
+  // TODO(alokp): Neuter m_buffer.
+  m_buffer = nullptr;
+}
+
+DEFINE_TRACE(MojoSharedBufferMapping) {
+  visitor->trace(m_buffer);
+}
+
+}  // namespace blink