Extract non-IO part of mksnapshot into an API method.

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 5343 matching lines @@
    * - To avoid unnecessary copies of data, V8 will point directly into the
    *   given data blob, so pretty please keep it around until V8 exit.
    * - Compression of the startup blob might be useful, but needs to
    *   handled entirely on the embedders' side.
    * - The call will abort if the data is invalid.
    */
   static void SetNativesDataBlob(StartupData* startup_blob);
   static void SetSnapshotDataBlob(StartupData* startup_blob);
 
   /**
+   * Create a new isolate and context for the purpose of capturing a snapshot
+   * Returns { NULL, 0 } on failure.
+   * The caller owns the data array in the return value.
+   */
+  static StartupData CreateSnapshotDataBlob();
+
+  /**
    * Adds a message listener.
    *
    * The same message listener can be added more than once and in that
    * case it will be called more than once for each message.
    *
    * If data is specified, it will be passed to the callback when it is called.
    * Otherwise, the exception object will be passed to the callback instead.
    */
   // TODO(dcarney): deprecate this.
   V8_INLINE static bool AddMessageListener(
@@ skipping 2124 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_