Issue #909 - Fixed: Update record in developer tools panel when assigning it a filter later

There are multiple listeners in adblockpluschrome/lib/requestBlocker.js in which requests are being blocked. When determining whether a new record should be added to the developer tools panel, we are checking whether the request has already been added and, if it has, whether the matched filter is considered a duplicate of the new filter that matches that same request.

However, in this particular case, the request has already been added, but without a filter, by an earlier listener (i.e. a browser.webRequest.onBeforeRequest listener). Therefore, when a filter matches that request later on (i.e. in a browser.webRequest.onHeadersReceived), we don't need to add a new record but update the existing one.