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

Review URL: https://codereview.chromium.org/841323002

Cr-Commit-Position: refs/heads/master@{#310863}

PRESUBMIT.py

@@ -357,53 +357,6 @@ def _CheckNoUNIT_TESTInSourceFiles(input_api, output_api):
   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):
   """Checks to make sure we don't introduce use of wstrings."""
@@ -1628,7 +1581,6 @@ def CheckChangeOnUpload(input_api, output_api):
   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))
   results.extend(
       input_api.canned_checks.CheckGNFormatted(input_api, output_api))
   return results

PRESUBMIT_test.py

@@ -270,28 +270,6 @@ class VersionControlConflictsTest(unittest.TestCase):
     self.assertTrue('3' in errors[1])
     self.assertTrue('5' in errors[2])
 
-class UmaHistogramChangeMatchedOrNotTest(unittest.TestCase):
-  def testTypicalNotMatchedChange(self):
-    diff = ['UMA_HISTOGRAM_BOOL("Bla.Foo.Dummy", true)']
-    mock_input_api = MockInputApi()
-    mock_input_api.files = [MockFile('some/path/foo.cc', diff)]
-    warnings = PRESUBMIT._CheckUmaHistogramChanges(mock_input_api,
-                                                   MockOutputApi())
-    self.assertEqual(1, len(warnings))
-    self.assertEqual('warning', warnings[0].type)
-
-  def testTypicalCorrectlyMatchedChange(self):
-    diff_cc = ['UMA_HISTOGRAM_BOOL("Bla.Foo.Dummy", true)']
-    diff_xml = ['<histogram name="Bla.Foo.Dummy"> </histogram>']
-    mock_input_api = MockInputApi()
-    mock_input_api.files = [
-      MockFile('some/path/foo.cc', diff_cc),
-      MockFile('tools/metrics/histograms/histograms.xml', diff_xml),
-    ]
-    warnings = []
-    warnings = PRESUBMIT._CheckUmaHistogramChanges(mock_input_api,
-                                                   MockOutputApi())
-    self.assertEqual(0, len(warnings))
 
 class BadExtensionsTest(unittest.TestCase):
   def testBadRejFile(self):