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This patch ensures that iterators cannot be copied..
Since we rely on a member heap that points to another member vector,
we can't do a naive copy. Instead we would have to reconstruct the
heap to point to the new members, but it's better to just restrict
copy altogether.

R=enne

Review URL: https://codereview.chromium.org/251003002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@267042 0039d316-1c4b-4281-b951-d872f2087c98