Auto merge of #1329 - glennw:gpu-cache-bug-fix, r=kvark
Auto merge of #1329 - glennw:gpu-cache-bug-fix, r=kvark

Fix a bug setting the gpu cache last access time.

The last access time for a block is initialized when the free
list for a row is created.

The bug manifests in the following way:
 * New row is allocated on frame 1 - blocks access time = 1
 * New display list is received on frame 2.
 * Blocks are allocated from the same row, but the last_access_time was not set.
 * A debug assert occurs during get_address - where it checks that the block was requested this frame.

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