Renamed some cache size constants that shared names.

Both the GPU image cache and the software image cache
used the same name for its cache size constants. This caused
collisions in jumbo builds where the cc files were
compiled together in the same translation unit.

Bug: 786956
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: Ic6a66f45daacc94040e1cc11410b85d674651548
Reviewed-on: https://chromium-review.googlesource.com/779401
Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#518228}
2 files changed