Add a version tag for cached data.

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 1220 matching lines @@
   /**
    * Compiles a streamed script (bound to current context).
    *
    * This can only be called after the streaming has finished
    * (ScriptStreamingTask has been run). V8 doesn't construct the source string
    * during streaming, so the embedder needs to pass the full source here.
    */
   static Local<Script> Compile(Isolate* isolate, StreamedSource* source,
                                Handle<String> full_source_string,
                                const ScriptOrigin& origin);
+
+  /**
+   * Return a version tag for CachedData for the current V8 version & flags.
+   *
+   * This value is meant only for determining whether a previously generated
+   * CachedData instance is still valid; the tag has no other meaing.
+   *
+   * Background: The data carried by CachedData may depend on the exact
+   *   V8 version number or currently compiler flags. This means when
+   *   persisting CachedData, the embedder must take care to not pass in
+   *   data from another V8 version, or the same version with different
+   *   features enabled.
+   *
+   *   The easiest way to do so is to clear the embedder's cache on any
+   *   such change.
+   *
+   *   Alternatively, this tag can be stored alongside the cached data and
+   *   compared when it is being used.
+   */
+  static uint32_t CachedDataVersionTag();
 };
 
 
 /**
  * An error message.
  */
 class V8_EXPORT Message {
  public:
   Local<String> Get() const;
   Local<String> GetSourceLine() const;
@@ skipping 6156 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_