Fix renderer kill resulting from tab discard logic.
Fix renderer kill resulting from tab discard logic.

BUG=121373
TEST=See bug, comment 24.

Review URL: https://chromiumcodereview.appspot.com/9992005

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@131002 0039d316-1c4b-4281-b951-d872f2087c98

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