Make mojob.py test succeed on Windows.

mojo/tools/test_runner.py

Index: mojo/tools/test_runner.py
diff --git a/mojo/tools/test_runner.py b/mojo/tools/test_runner.py
index 28eb3bedc0df6606bbebea048bd3af9ed4a708db..ea892af363301b4723c4872103bd2f379970e399 100755
--- a/mojo/tools/test_runner.py
+++ b/mojo/tools/test_runner.py
@@ -7,6 +7,7 @@
 
 import logging
 import os
+import platform
 import subprocess
 import sys
 
@@ -71,6 +72,9 @@ def main(argv):
     else:
       cacheable = True
 
+    if platform.system() == 'Windows':
+      gtest += ".exe"
+
     if successes_cache_file and cacheable:
       _logging.debug("Getting transitive hash for %s ... " % gtest)
       try: