Partial revert of "Added metrics to count the number of items in the shelf."

Partial revert of "Added metrics to count the number of items in the shelf."

Collecting the metrics was sometimes causing a crash and has been removed
until the root cause is found.
This is only a partial revert because items are not to be removed from
tools/metrics/histograms/histograms.xml.

BUG=474702
Committed: https://crrev.com/917c61c1a5859243b159c86d42c4d8f7f523412d
Cr-Commit-Position: refs/heads/master@{#324226}

[bruthig, 2015-04-08 13:01:44]

bruthig@chromium.org changed reviewers:
+ derat@chromium.org

[bruthig, 2015-04-08 13:01:44]

derat@, can you please have a look?

[Daniel Erat, 2015-04-08 13:02:59]

lgtm

[bruthig, 2015-04-08 13:03:43]

The CQ bit was checked by bruthig@chromium.org

[commit-bot: I haz the power, 2015-04-08 13:03:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1070693002/1

[commit-bot: I haz the power, 2015-04-08 14:37:44]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-08 14:38:35]

Patchset 1 (id:??) landed as
https://crrev.com/917c61c1a5859243b159c86d42c4d8f7f523412d
Cr-Commit-Position: refs/heads/master@{#324226}