Delay releasing plugin process for 10s.
Delay releasing plugin process for 10s.

Change plugin process release from immediately after
we navigate away from our last plugin reference to a
task that is run 10s later.

Original patch by John Abd-El-Malek (jam@chromium.org).

BUG=11341
TEST=Open Chrome, load youtube.com, click Videos,
verify all pages load correctly.

Review URL: http://codereview.chromium.org/164157

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@22818 0039d316-1c4b-4281-b951-d872f2087c98

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