Introduce extras export object.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index d4b664a5495a2481f3db61274be6ef6948889371..3ba8065bc98764d0fd24644ea134f20f895b6589 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -6372,6 +6372,13 @@ class V8_EXPORT Context {
   V8_INLINE Local<Value> GetEmbedderData(int index);
 
   /**
+   * Gets the exports object used by V8 extras. Extra natives get a reference
+   * to this object and can use it to export functionality.
+   * If there are no extra native scripts, return an emtpy handle.
+   */
+  MaybeLocal<Object> GetExtrasExportsObject();

[domenic, 2015/05/18 16:43:11]

FYI I wasn't sure whether to use MaybeLocal or Local. MaybeLocal is new and cool
but other methods of this class all return Locals.

[Yang, 2015/05/18 18:30:55]

You are right. At first I had a version where we could have undefined as extras
object, if there are no extra scripts, in which case we would return an empty
handle. Then I changed my mind, but forgot this part. I will change this and
update the comment.

+
+  /**
    * Sets the embedder data with the given index, growing the data as
    * needed. Note that index 0 currently has a special meaning for Chrome's
    * debugger.