Fix broken "gcl diff cl" command. We need to use full paths, not

relative path. 

bug:45589
Review URL: http://codereview.chromium.org/2447002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@48680 0039d316-1c4b-4281-b951-d872f2087c98

gcl.py

@@ -1166,8 +1166,12 @@ def CMDdiff(args):
     files = change_info.GetFileNames()
   else:
     files = GetFilesNotInCL()
-  return RunShellWithReturnCode(['svn', 'diff'] + files + args,
-                                print_output=True)[1]
+
+  root = GetRepositoryRoot()
+  cmd = ['svn', 'diff']
+  cmd.extend([os.path.join(root, x) for x in files])
+  cmd.extend(args)
+  return RunShellWithReturnCode(cmd, print_output=True)[1]
 
 
 @no_args