Have DOMImplementation::document() return reference.

Source/bindings/tests/idls/TestInterfacePython3.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 15 matching lines @@
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  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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 // This is for interface extended attributes that interact with another extended
 // attribute, and thus both cannot be tested at once.
 // The more *minor* extended attribute should be put in this file.
 
 [
-    Custom=VisitDOMWrapper,  // Conflict with [SetWrapperReferenceTo] and [SetWrapperReferenceFrom]
+    SetWrapperReferenceFromReference=document,  // Conflicts with [SetWrapperReferenceFrom]

[Inactive, 2014/02/21 00:41:39]

Please create a new test IDL file instead of editing an existing one. We don't
want to loose coverage for anything. Also, I don't think we should mess with the
ones with "Python" in the name. Just add a new IDL such as
"TestSetWrapperReferenceFromReference.idl".

Also, don't forget to use this copyright header for the new idl:
https://sites.google.com/a/chromium.org/dev/blink/coding-style#TOC-License

[Nils Barth (inactive), 2014/02/21 01:13:48]

To follow-up to what Chris said:

On 2014/02/21 00:41:39, Chris Dumez wrote:
Please do *not* delete existing tests:
your change removes the test for [Custom=VisitDOMWrapper]
Not LGTM.
That's a fine guideline, but basically "Python" means
"new, better organized test cases";
the Python IDL compiler now tests and passes everything except TestSVG.idl.
(Just need to clean up the test files, as there's a lot of
small ones and duplication.)
For consistency and simplicity, you can call it TestInterface2.idl
(this means we can reuse it for other extended attributes)

Given that this is "yet another wrapper extended attribute on interfaces", could
you actually put this in
TestInterfacePython4.idl
with the comment:
// Conflicts with [SetWrapperReferenceTo], [SetWrapperReferenceFrom], and
[Custom=VisitDOMWrapper]

Thanks!

 ] interface TestInterfacePython3 {
 };