Add PRESUBMIT check if modified UMA histogram name can be found

Add PRESUBMIT check if modified UMA histogram name can be found

This Presubmit checks if some diffs affect any UMA_HISTOGRAM_*
macro and, if so, checks if the histogram name is to be found
in either tools/metrics/histograms/histograms.xml or in the
CL diffs.

Addresses the problem of someone modifying code and
inadvertently forgetting a corresponding histograms.xml
adaptation, that has happened in the past.

BUG=434420
Committed: https://crrev.com/2ece5270462346b1ac3bccd3bfe5e68d024b98b5
Cr-Commit-Position: refs/heads/master@{#306388}

[mcasas, 2014-11-28 19:42:10]

mcasas@chromium.org changed reviewers:
+ phajdan.jr@chromium.org

[mcasas, 2014-11-28 19:42:11]

phajdan.jr@ Low Prio Review, PTAL

[mcasas, 2014-11-28 19:44:04]

Patchset #1 (id:1) has been deleted

[Paweł Hajdan Jr., 2014-12-01 11:59:07]

https://codereview.chromium.org/766713004/diff/20001/PRESUBMIT.py
File PRESUBMIT.py (right):

https://codereview.chromium.org/766713004/diff/20001/PRESUBMIT.py#newcode378
PRESUBMIT.py:378: touched_histograms.append([found.group(1), f, line_num]);
nit: Remove the semicolon

https://codereview.chromium.org/766713004/diff/20001/PRESUBMIT.py#newcode392
PRESUBMIT.py:392: with open('tools/metrics/histograms/histograms.xml') as
histograms_xml:
Why not parse the XML?

[mcasas, 2014-12-01 19:41:37]

PTAL

https://codereview.chromium.org/766713004/diff/20001/PRESUBMIT.py
File PRESUBMIT.py (right):

https://codereview.chromium.org/766713004/diff/20001/PRESUBMIT.py#newcode378
PRESUBMIT.py:378: touched_histograms.append([found.group(1), f, line_num]);
On 2014/12/01 11:59:07, Paweł Hajdan Jr. wrote:
> nit: Remove the semicolon

Done.

https://codereview.chromium.org/766713004/diff/20001/PRESUBMIT.py#newcode392
PRESUBMIT.py:392: with open('tools/metrics/histograms/histograms.xml') as
histograms_xml:
On 2014/12/01 11:59:07, Paweł Hajdan Jr. wrote:
> Why not parse the XML?

I don't think we need to understand the whole XML,
just make sure there's a histogram name match. Parse
would be overkill here.

[Paweł Hajdan Jr., 2014-12-02 10:29:19]

LGTM

[mcasas, 2014-12-02 15:02:18]

The CQ bit was checked by mcasas@chromium.org

[commit-bot: I haz the power, 2014-12-02 15:03:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/766713004/40001

[commit-bot: I haz the power, 2014-12-02 15:37:32]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2014-12-02 15:38:18]

Patchset 2 (id:??) landed as
https://crrev.com/2ece5270462346b1ac3bccd3bfe5e68d024b98b5
Cr-Commit-Position: refs/heads/master@{#306388}

[Alexei Svitkine (slow), 2015-01-09 15:39:20]

A revert of this CL (patchset #2 id:40001) has been created in
https://codereview.chromium.org/841323002/ by asvitkine@chromium.org.

The reason for reverting is: Produces false positive warnings on histograms
using histogram_suffixes, see:

https://code.google.com/p/chromium/issues/detail?id=445265.