The files_to_skip lists in chrome/android/java/src/PRESUBMIT.py were
not working on Windows because they didn't use the verbose [\\\/]
construct for path separators. Fixing this in FilterSourceFile means
that multiple failures may be fixed simultaneously. The only failures
that this is known to fix are a set of AlertDialog.Builder errors that
were showing up only on Windows.

This addresses the issues that were going to be incorrectly fixed in
crrev.com/c/3606128 (now abandoned).

Bug: 1309977
Change-Id: I7a10483448e00df55e2cbf8bff8bad7a5d8db124
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3609117Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>