[Telemetry] Fix histogram naming.

[Telemetry] Fix histogram naming.

trace_tags should show up on the trace names but not the chart names. Previously
we'd output:
HISTOGRAM V8.MemoryHeapSampleTotalUsed_foo: V8.MemoryHeapSampleTotalUsed_foo=

Now we output:
HISTOGRAM V8.MemoryHeapSampleTotalUsed: V8.MemoryHeapSampleTotalUsed_foo=

This prevents an explosion of charts as seen on:
http://build.chromium.org/f/chromium/perf/linux-release/moz/report.html?history=150&rev=-1&graph=V8.MemoryExternalFragmentationTotal_extcs1_0.5

BUG=196411
TEST=tools/perf/run_multipage_benchmarks --browser=system page_cycler tools/perf/page_sets/page_cycler/moz.json --output-trace-tag=_foo
NOTRY=True


Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=189022

[tonyg, 2013-03-19 00:56:33]

ptal

[marja, 2013-03-19 01:00:11]

So this would put lines for different pages into the same graph? I'm not sure if
that makes sense, it might just make the graphs hard to read. (Hopefully the
graphs would be separate, in which case it would be possible to read, but what
if they're approx. the same values...?)

[tonyg, 2013-03-19 01:04:58]

On 2013/03/19 01:00:11, marja wrote:
> So this would put lines for different pages into the same graph? I'm not sure
if
> that makes sense, it might just make the graphs hard to read. (Hopefully the
> graphs would be separate, in which case it would be possible to read, but what
> if they're approx. the same values...?)

It won't put different pages on the same graph. Just different build types. For
instance, the reference build.

[marja, 2013-03-19 03:56:48]

Ah, k. lgtm.

[commit-bot: I haz the power, 2013-03-19 15:36:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tonyg@chromium.org/12900005/2001

[commit-bot: I haz the power, 2013-03-19 15:36:40]

Change committed as 189022