bindings: Fix bindings generation in Windows.

The generated EventNames.in file was having \s in the event-names, which
didn't match the names in EventAliases.in (which have /s). So make sure
to replace the '\'s with '/'s in filenames when writing them to EventNames.in.

BUG=256230
R=ch.dumez@sisa.samsung.com

Review URL: https://codereview.chromium.org/19373005

git-svn-id: svn://svn.chromium.org/blink/trunk@154326 bbb929c8-8fbe-4397-9dbb-9b2b20218538