Add a RELEASE_ASSERT to guard against duplicates in DOMWrapperMap
Add a RELEASE_ASSERT to guard against duplicates in DOMWrapperMap

Now that crbug.com/85158 and crbug.com/87520 are fixed, there should be no
way to leak objects across isolated worlds. And thus no known way of ending
up with duplicates in the DOMWrapperMap. To test that assumption, this patch
adds a RELEASE_ASSERT that the object for which we're creating a newly-created
wrapper doesn't currently appear in the DOMWrapperMap.

R=abarth

Review URL: https://chromiumcodereview.appspot.com/18860004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@153736 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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