Fix some grammatical errors in comments in tools/

tools/dromaeo_benchmark_runner/dromaeo_benchmark_runner.py

 #!/usr/bin/env python
 # Copyright (c) 2011 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.
 
 """Dromaeo benchmark automation script.
 
 Script runs dromaeo tests in browsers specified by --browser switch and saves
 results to a spreadsheet on docs.google.com.
 
 Prerequisites:
 1. Install Google Data APIs Python Client Library from
    http://code.google.com/p/gdata-python-client.
 2. Checkout Dromaeo benchmark from
    http://src.chromium.org/svn/trunk/src/chrome/test/data/dromaeo and provide
    local path to it in --dromaeo_home switch.
-3. Create a spreadsheet at http://docs.google.com and specify it's name in
+3. Create a spreadsheet at http://docs.google.com and specify its name in
    --spreadsheet switch
 
 Benchmark results are presented in the following format:
 browser | date time
 test 1 name|m11|...|m1n|test 1 average mean| |e11|...|e1n|test 1 average error
 test 2 name|m21|...|m2n|test 2 average mean| |e21|...|e2n|test 2 average error
 ...
 
 Here mij is mean run/s in individual dromaeo test i during benchmark run j,
 eij is error in individual dromaeo test i during benchmark run j.
@@ skipping 229 matching lines @@
     # Insert test results into spreadsheet.
     for (test_name, test_data) in benchmark_results.data.iteritems():
       spreadsheet_writer.WriteBrowserBenchmarkResults(test_name, test_data)
 
   server.socket.close()
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())