Revert of Add PRESUBMIT check if modified UMA histogram name can be found

Revert of Add PRESUBMIT check if modified UMA histogram name can be found (patchset #2 id:40001 of https://codereview.chromium.org/766713004/)

Reason for revert:
Produces false positive warnings on histograms using histogram_suffixes, see:

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

Original issue's description:
> 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}

TBR=phajdan.jr@chromium.org,mcasas@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=434420, 445265
Committed: https://crrev.com/e56a58d717f0ee53671d80518c9bcf70824a4d63
Cr-Commit-Position: refs/heads/master@{#310863}

[Alexei Svitkine (slow), 2015-01-09 15:39:21]

Created Revert of Add PRESUBMIT check if modified UMA histogram name can be
found

[commit-bot: I haz the power, 2015-01-09 15:40:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/841323002/1

[commit-bot: I haz the power, 2015-01-09 15:41:07]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-09 15:41:08]

Failed to apply patch for PRESUBMIT.py:
While running git apply --index -3 -p1;
  error: patch failed: PRESUBMIT.py:1567
  Falling back to three-way merge...
  Applied patch to 'PRESUBMIT.py' with conflicts.
  U PRESUBMIT.py

Patch:       PRESUBMIT.py
Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index
6762e2775e461be1d8d90598d060d252ea7168c8..90d1df4e286eaad7dac54b35f082b83609c7b5bc
100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -356,53 +356,6 @@
     return []
   return [output_api.PresubmitPromptWarning('UNIT_TEST is only for headers.\n'
+
       '\n'.join(problems))]
-
-def _CheckUmaHistogramChanges(input_api, output_api):
-  """Check that UMA histogram names in touched lines can still be found in
other
-  lines of the patch or in histograms.xml. Note that this check would not catch
-  the reverse: changes in histograms.xml not matched in the code itself."""
-
-  touched_histograms = []
-  histograms_xml_modifications = []
-  pattern = input_api.re.compile('UMA_HISTOGRAM.*\("(.*)"')
-  for f in input_api.AffectedFiles():
-    # If histograms.xml itself is modified, keep the modified lines for later.
-    if (f.LocalPath().endswith(('histograms.xml'))):
-      histograms_xml_modifications = f.ChangedContents()
-      continue
-    if (not f.LocalPath().endswith(('cc', 'mm', 'cpp'))):
-      continue
-    for line_num, line in f.ChangedContents():
-      found = pattern.search(line)
-      if found:
-        touched_histograms.append([found.group(1), f, line_num])
-
-  # Search for the touched histogram names in the local modifications to
-  # histograms.xml, and if not found on the base file.
-  problems = []
-  for histogram_name, f, line_num in touched_histograms:
-    histogram_name_found = False
-    for line_num, line in histograms_xml_modifications:
-      if histogram_name in line:
-        histogram_name_found = True;
-        break;
-    if histogram_name_found:
-      continue
-
-    with open('tools/metrics/histograms/histograms.xml') as histograms_xml:
-      for line in histograms_xml:
-        if histogram_name in line:
-          histogram_name_found = True;
-          break;
-    if histogram_name_found:
-      continue
-    problems.append(' [%s:%d] %s' % (f.LocalPath(), line_num, histogram_name))
-
-  if not problems:
-    return []
-  return [output_api.PresubmitPromptWarning('Some UMA_HISTOGRAM lines have '
-    'been modified and the associated histogram name has no match in either '
-    'metrics/histograms.xml or the modifications of it:',  problems)]
 
 
 def _CheckNoNewWStrings(input_api, output_api):
@@ -1567,7 +1520,6 @@
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(_CheckValidHostsInDEPS(input_api, output_api))
   results.extend(_CheckJavaStyle(input_api, output_api))
-  results.extend(_CheckUmaHistogramChanges(input_api, output_api))
   return results

[commit-bot: I haz the power, 2015-01-09 15:41:34]

The CQ bit was unchecked by commit-bot@chromium.org

[Alexei Svitkine (slow), 2015-01-09 21:41:30]

The CQ bit was checked by asvitkine@chromium.org

[commit-bot: I haz the power, 2015-01-09 21:42:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/841323002/70001

[commit-bot: I haz the power, 2015-01-09 21:44:21]

Committed patchset #2 (id:70001)

[commit-bot: I haz the power, 2015-01-09 21:45:55]

Patchset 2 (id:??) landed as
https://crrev.com/e56a58d717f0ee53671d80518c9bcf70824a4d63
Cr-Commit-Position: refs/heads/master@{#310863}