SimpleCache: fix error in computation of crc32 for stream 0

SimpleCache: fix error in computation of crc32 for stream 0

This CL fixes the following problem:
1) An EOF record for stream 0 is written to disk with no crc32.
2) The entry is opened, and the wrong crc32 (from the EOF records, that is
invalid) is assigned as the computed value for stream 0.
3) Something is written to stream1 but not to stream 0 and the entry is closed.
An EOF record needs to be written for stream 0, where the HAS_CRC32 flag is on,
but which has the wrong value.
4) Next open will fail because of wrong value of crc32 for stream 0.

BUG=173398
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=224138

[clamy, 2013-09-19 13:00:33]

pasko, gavinp: PTAL

Found this while working on the testing CL. I guess I should improve my variable
naming skills to avoid this kind of mistake.

[pasko, 2013-09-19 13:06:33]

lgtm

LGTM

great catch!

since this depends on stream0 not being written in sequence, I guess this does
not happen in practice, but I'd really like to commit this ASAP anyway. The test
is being worked on and "slightly" depends on the multiple stream testing, it
would be a little more work to extract it. TBD.

[commit-bot: I haz the power, 2013-09-19 13:06:46]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/clamy@chromium.org/24251005/1

[commit-bot: I haz the power, 2013-09-19 15:44:48]

Change committed as 224138