Don't purge resources from cache if they have > 1 ref

The gpu cache behavior changes as expected from this CL (i.e., the high water marks increase but everything else remains the same). The msaa16 cache behavior changes a bit oddly. The high water marks change appropriately but the current counts also change. I believe this is due to msaa16 always exceeding the cache limit so everything was always being purged but now some items are retained in the cache.

without this CL:

config: gpu 1fad70
Budget: 256 items 16777216 bytes
                Entry Count: current 21 high 108
                Unlocked Entry Count: current 11 high 100
                Entry Bytes: current 15745476 high 37604236
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

with this CL:

config: gpu 832138
Budget: 256 items 16777216 bytes
                Entry Count: current 21 high 163
                Unlocked Entry Count: current 11 high 162
                Entry Bytes: current 15745476 high 198836800
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

without this CL:

config: msaa16 95ad70
Budget: 256 items 16777216 bytes
                Entry Count: current 2 high 17
                Unlocked Entry Count: current 0 high 10
                Entry Bytes: current 9401600 high 120365568
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

with this CL:

config: msaa16 6b2138
Budget: 256 items 16777216 bytes
                Entry Count: current 13 high 164
                Unlocked Entry Count: current 1 high 162
                Entry Bytes: current 228556032 high 317456128
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

[bsalomon, 2012-09-04 13:14:24]

On 2012/08/31 19:07:40, robertphillips wrote:

LGTM

[robertphillips, 2012-09-04 13:36:49]

committed as r5380