Avoid hard-coded Linux path in grit test expectations

Many of the grit presubmits fail on Windows. This fixes one of them by
replacing a hard-coded Linux path with os.path.join.

Change-Id: I1e2944f617369efa13bc64dc6e4163d38c12e490
Reviewed-on: https://chromium-review.googlesource.com/c/1484812
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634909}

tools/grit/grit/format/resource_map_unittest.py

@@ -109,13 +109,14 @@ const size_t kTheRcHeaderSize = base::size(kTheRcHeader);''', output)
 
     formatter = resource_map.GetFormatter('gzipped_resource_file_map_source')
     output = util.StripBlankLinesAndComments(''.join(formatter(grd, 'en', '.')))
+    gen_path = os.path.join('@out_folder@', 'gen', 'foo', 'bar', 'baz.js')
     expected = '''\
 #include "gzipped_resource_map_header.h"
 #include <stddef.h>
 #include "base/stl_util.h"
 #include "the_rc_header.h"
 const GzippedGritResourceMap kTheRcHeader[] = {
-  {"@out_folder@/gen/foo/bar/baz.js", IDR_FOO_BAR_BAZ_JS, true},
+  {"''' + gen_path + '''", IDR_FOO_BAR_BAZ_JS, true},
 };
 const size_t kTheRcHeaderSize = base::size(kTheRcHeader);'''
     self.assertEqual(expected, output)