Implements JS bindings for mojo shared buffer.

third_party/WebKit/Source/core/mojo/MojoMapBufferResult.idl

Index: third_party/WebKit/Source/core/mojo/MojoMapBufferResult.idl
diff --git a/third_party/WebKit/Source/core/mojo/MojoMapBufferResult.idl b/third_party/WebKit/Source/core/mojo/MojoMapBufferResult.idl
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+// 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.
+
+dictionary MojoMapBufferResult {
+    required MojoResult result;
+
+    // TODO(alokp): Consider wrapping the buffer into a MojoSharedBufferMapping
+    // that would expose an unmap method to free the shared buffer eagerly
+    // rather than waiting for GC. This would be similar to ImageBitmap.close
+    // that disposes of graphical resources.
+    ArrayBuffer buffer;
+};