Don't assert if PP already contains a valid PP callback. The PP can handle multiple callbacks (using PPChainedCallbacks)
Don't assert if PP already contains a valid PP callback. The PP can handle multiple callbacks (using PPChainedCallbacks)

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@97910 91177308-0d34-0410-b5e6-96231b3b80d8

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