content: Crash key and trace counter cleanup.

content: Crash key and trace counter cleanup.

Sort fixed_keys[] properly and improve the name of the
crash keys to make it easy for someone not familiar
with discardable memory to understand what they are.

Also use TRACE_COUNTER1 instead of TRACE_COUNTER_ID1
for TotalDiscardableMemoryUsage as there should never
be more than one of these per process.

BUG=

Committed: https://crrev.com/bab0737d3087f548e8bbe615adf5c83e2bcddc47
Cr-Commit-Position: refs/heads/master@{#321786}

[reveman, 2015-03-23 15:04:20]

reveman@chromium.org changed reviewers:
+ avi@chromium.org, rsesek@chromium.org

[Robert Sesek, 2015-03-23 15:13:39]

LGTM

[Avi (use Gerrit), 2015-03-23 15:19:49]

The CQ bit was checked by avi@chromium.org

[Avi (use Gerrit), 2015-03-23 15:19:49]

lgtm

[commit-bot: I haz the power, 2015-03-23 15:20:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1028853002/20001

[commit-bot: I haz the power, 2015-03-23 16:12:08]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-23 16:12:51]

Patchset 2 (id:??) landed as
https://crrev.com/bab0737d3087f548e8bbe615adf5c83e2bcddc47
Cr-Commit-Position: refs/heads/master@{#321786}