Check if the given root path argument points to a valid directory. Display an error message and quit if it is not.

Review URL: http://codereview.chromium.org/118379

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@17856 0039d316-1c4b-4281-b951-d872f2087c98

chrome-update.py

@@ -144,6 +144,9 @@ def Main():
     sys.exit(1)
 
   chrome_root = args[0]
+  if not os.path.isdir(chrome_root):
+    Message("Path to chrome root (%s) not found." % repr(chrome_root))
+    sys.exit(1)
 
   if not options.nosync:
     rv = DoUpdate(chrome_root)