Add high-precision timing histograms.

tools/metrics/histograms/pretty_print.py

 #!/usr/bin/env python
 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Pretty-prints the histograms.xml file, alphabetizing tags, wrapping text
 at 80 chars, enforcing standard attribute ordering, and standardizing
 indentation.
 
 This is quite a bit more complicated than just calling tree.toprettyxml();
@@ skipping 14 matching lines @@
 import presubmit_util
 
 import print_style
 
 
 class Error(Exception):
   pass
 
 
 UNIT_REWRITES = {
+  'microsecond': 'microseconds',
+  'us': 'microseconds',
   'millisecond': 'ms',
   'milliseconds': 'ms',
   'kb': 'KB',
   'kB': 'KB',
   'kilobytes': 'KB',
   'kbits/s': 'kbps',
   'percent': '%',
   'Percent': '%',
   'percentage': '%',
 }
@@ skipping 32 matching lines @@
   return print_style.GetPrintStyle().PrettyPrintXml(tree)
 
 
 def main():
   presubmit_util.DoPresubmitMain(sys.argv, 'histograms.xml',
                                  'histograms.before.pretty-print.xml',
                                  'pretty_print.py', PrettyPrint)
 
 if __name__ == '__main__':
   main()