Fix a break in drover.py that prevented webkit merges.

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@59179 0039d316-1c4b-4281-b951-d872f2087c98

drover.py

@@ -402,9 +402,11 @@ def drover(options, args):
   # Override the default properties if there is a drover.properties file.
   global file_pattern_
   if os.path.exists("drover.properties"):
-    FILE_PATTERN = file_pattern_
-    execfile("drover.properties")
-    file_pattern_ = FILE_PATTERN
+    f = open("drover.properties")
+    exec(f)
+    f.close()
+    if FILE_PATTERN:
+      file_pattern_ = FILE_PATTERN
 
   if options.revert and options.branch:
     url = BRANCH_URL.replace("$branch", options.branch)