Bug 1046984. Include the stride in the gralloc memory report.

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extra : rebase_source : b5c7f060c73dc67b4cdb3fe29a59c288ddbde9b2
Bug 1044241. Discard tile back buffers that haven't been recently used. r=nical

Tracks tiles that have a back buffer with a nsExpirationTracker and discards
them after a while. This should help us claim back tile memory for tiles
that have stopped changing.

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extra : rebase_source : 2528de0a6fac08cb6f97ebd946d9f72a63b7d2b1