Add support to extension_shell and ash_shell to use external V8 snapshot files.

gin/v8_initializer.h

 // Copyright 2013 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.
 
 #ifndef GIN_V8_INITIALIZER_H_
 #define GIN_V8_INITIALIZER_H_
 
 #include "base/files/file.h"
 #include "gin/array_buffer.h"
 #include "gin/gin_export.h"
@@ skipping 31 matching lines @@
                                    int64 natives_offset,
                                    int64 natives_size,
                                    base::PlatformFile snapshot_fd,
                                    int64 snapshot_offset,
                                    int64 snapshot_size);
 
   // Load V8 snapshot from default resources. Returns true on success or
   // snapshot is already loaded, false otherwise.
   static bool LoadV8Snapshot();
 
+  // Opens the V8 snapshot data files and returns open file descriptors to these
+  // files in |natives_fd_out| and |snapshot_fd_out|, which can be passed to
+  // child processes.
+  static bool OpenV8FilesForChildProcesses(base::PlatformFile* natives_fd_out,
+                                           base::PlatformFile* snapshot_fd_out);
+
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 };
 
 }  // namespace gin
 
 #endif  // GIN_V8_INITIALIZER_H_