Refactor some code in tools/metrics/histograms directory

Change-Id: I67a0f21df7e3becd2e76e4971d040e9c1c4138ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354725
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798297}

tools/metrics/histograms/histogram_ownership.py

@@ -9,7 +9,6 @@ histograms.
 
 from __future__ import print_function
 
-import errno
 import os
 import sys
 from xml.etree import ElementTree as ET
@@ -18,6 +17,9 @@ import extract_histograms
 import histogram_paths
 import merge_xml
 
+sys.path.append(os.path.join(os.path.dirname(__file__), 'common'))
+import path_util
+
 
 def PrintOwners(root):
   assert root.tag == 'histogram-configuration'
@@ -67,13 +69,14 @@ def main():
     python histogram_ownership.py
   """
   if len(sys.argv) == 1:
-    merged_xml_string = merge_xml.PrettyPrintMergedFiles(
-        histogram_paths.ALL_XMLS)
+    merged_xml_string = merge_xml.MergeFiles(
+        histogram_paths.ALL_XMLS).toxml()
     root = ET.fromstring(merged_xml_string)
   else:
-    rel_path = sys.argv[1]
+    rel_path = path_util.GetInputFile(
+        os.path.join('tools', 'metrics', 'histograms', sys.argv[1]))
     if not os.path.exists(rel_path):
-      raise FileNotFoundError(errno.ENOENT, os.strerror(errno.ENOENT))
+      raise ValueError("A histograms.xml file does not exist in %s" % rel_path)
 
     tree = ET.parse(rel_path)
     root = tree.getroot()

tools/metrics/histograms/split_xml.py

@@ -7,7 +7,6 @@ Splits nodes according to the first camelcase part of their name attribute.
 Intended to be used to split up the large histograms.xml or enums.xml file.
 """
 
-import errno
 import logging
 import os
 import sys
@@ -40,8 +39,7 @@ def _ParseHistogramsXMLFile(base_dir):
     FileNotFoundError if histograms.xml not found in |base_dir|.
   """
   if HISTOGRAMS_XML not in os.listdir(base_dir):
-    raise FileNotFoundError(errno.ENOENT, os.strerror(errno.ENOENT),
-                            HISTOGRAMS_XML)
+    raise ValueError(HISTOGRAMS_XML + 'is not in %s' % base_dir)
 
   dom = minidom.parse(os.path.join(base_dir, HISTOGRAMS_XML))
   comments = []