Fix histogram_paths.py on Windows

There's 2 issues with histogram_paths.py on Windows:
  - Some path have different casing on Win vs Linux, see
    crbug.com/1132974 . This is not the right way to fix this but this
    allows running histogram_paths.py on Windows.
  - Normalizing the path separators after sorting them causes some
    sorting differences (this causes
    "tools/metrics/histograms/histograms_xml/renderer4/histograms.xml"
    to appear before
    "tools/metrics/histograms/histograms_xml/renderer/histograms.xml" on
    Windows.


Bug: 1132974
Change-Id: Id6953f29f2073551df9a13cc2c72d2e6eef33cd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2436293Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811401}

tools/metrics/histograms/histogram_paths.py

@@ -13,17 +13,18 @@ import path_util
 
 def _FindHistogramsXmlFiles():
   """Gets a list relative path to all histograms xmls under histograms_xml/."""
-  file_list = []
-  for dirName, _, fileList in os.walk(PATH_TO_HISTOGRAMS_XML_DIR):
-    for filename in fileList:
+  files = []
+  for dir_name, _, file_list in os.walk(PATH_TO_HISTOGRAMS_XML_DIR):
+    for filename in file_list:
       if (filename == 'histograms.xml'
           or filename == 'histogram_suffixes_list.xml'):
         # Compute the relative path of the histograms xml file.
-        file_path = os.path.relpath(os.path.join(dirName, filename),
+        file_path = os.path.relpath(os.path.join(dir_name, filename),
                                     PATH_TO_HISTOGRAMS_XML_DIR)
-        file_list.append(
-            os.path.join('tools/metrics/histograms/histograms_xml', file_path))
-  return sorted(file_list)
+        files.append(
+            os.path.join('tools/metrics/histograms/histograms_xml',
+                         file_path).replace(os.sep, '/').lower())
+  return sorted(files)
 
 
 ENUMS_XML_RELATIVE = 'tools/metrics/histograms/enums.xml'