Add a way to monitor cache hits and misses for deferred decoding.

Add a way to monitor cache hits and misses for deferred decoding.

Adds a new flag to bench_pictures in order to do this. Also fix
a warning.

Committed: https://code.google.com/p/skia/source/detail?r=7965

[reed1, 2013-03-04 19:54:43]

lgtm

[scroggo, 2013-03-04 19:56:39]

Committed patchset #2 manually as r7965 (presubmit successful).