[Bindings] Create and use V8 context snapshots

content/public/common/content_descriptor_keys.cc

 // 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 "content/public/common/content_descriptor_keys.h"
 
 namespace content {
 
 const char kV8NativesDataDescriptor[] = "v8_natives_data";
 
 const char kV8SnapshotDataDescriptor[] = "v8_snapshot_data";
 
 const char kV8Snapshot32DataDescriptor[] = "v8_snapshot_32_data";
 
 const char kV8Snapshot64DataDescriptor[] = "v8_snapshot_64_data";
 
-}  // namespace content
+const char kV8ContextSnapshotDataDescriptor[] = "v8_context_snapshot_data";
+
+}  // namespace content