Revert of Implement cache counting for the simple and memory backends.

Revert of Implement cache counting for the simple and memory backends. (patchset #3 id:40001 of https://codereview.chromium.org/1398053002/ )

Reason for revert:
Causes test failures on XP bot:
https://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/40465/steps/net_unittests%20on%20Windows-XP-SP3/logs/DiskCacheBackendTest.SimpleCacheCalculateSizeOfAllEntries

DiskCacheBackendTest.SimpleCacheCalculateSizeOfAllEntries (run #1):
[ RUN      ] DiskCacheBackendTest.SimpleCacheCalculateSizeOfAllEntries
c:uild\slave\win_builderuild\src
et\disk_cacheackend_unittest.cc(1730): error: Value of: result
  Actual: 7447
Expected: (count - 1) * count / 2 + total_metadata_size
Which is: 7455
c:uild\slave\win_builderuild\src
et\disk_cacheackend_unittest.cc(1747): error: Value of: new_result
  Actual: 8243
Expected: result + last_entry_size + GetEntryMetadataSize(key)
Which is: 8235
c:uild\slave\win_builderuild\src
et\disk_cacheackend_unittest.cc(1751): error: Value of: new_result
  Actual: 7455
Expected: result
Which is: 7447
[  FAILED  ] DiskCacheBackendTest.SimpleCacheCalculateSizeOfAllEntries (171 ms)

Original issue's description:
> Implement cache counting for the simple and memory backends.
>
> This is a followup to https://codereview.chromium.org/1304363013/, which implemented it for the blockfile backend.
>
> BUG=510028
>
> Committed: https://crrev.com/a319545886d0e297b88301f01b804432bea602f7
> Cr-Commit-Position: refs/heads/master@{#354037}

TBR=gavinp@chromium.org,pasko@chromium.org,ttuttle@chromium.org,msramek@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=510028
Committed: https://crrev.com/81c61dd0811b103aeca08e1a5184db725fdb19fb
Cr-Commit-Position: refs/heads/master@{#354118}

[Mark P, 2015-10-14 21:33:55]

Created Revert of Implement cache counting for the simple and memory backends.

[commit-bot: I haz the power, 2015-10-14 21:34:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1401053004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1401053004/1

[commit-bot: I haz the power, 2015-10-14 21:35:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-14 21:37:01]

Patchset 1 (id:??) landed as
https://crrev.com/81c61dd0811b103aeca08e1a5184db725fdb19fb
Cr-Commit-Position: refs/heads/master@{#354118}

[msramek, 2015-10-15 09:49:00]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1401923006/ by msramek@chromium.org.

The reason for reverting is: The original CL was reverted because of a failing
unittest. The results in the unittest are off by 8 bytes. 8 bytes is the size of
the second-to-last entry, which is the last one where we wrote to the stream #1.
As the comment in this unittest already mentions, writing to the stream #1
triggers another operation that is asynchronous and can possibly happen after
the call to CalculateSizeOfAllEntries. Apparently, this didn't happen on Linux,
but it did happen on Windows.

The test can be fixed by only writing to the stream #0..