This adds a "filteredMessagesCount" property to the messages store,
which is updated at the same time as we update the "visibleMessages"
property.
The global number of hidden messages is then shown next to the text search
input, and a button can be clicked to Reset the filters to their original
values.
This only takes into account messages that are filtered-out because
the default filters changes. Which means that non-default filters, like
CSS, Network and XHR don't impact filteredMessagesCount.
We take this as an opportunity to rename the match*Filter functions to
pass*Filter, since it better represents what the function does (a network
message is not impacted by a level filter, but it can be misleading to say
that it matches level filters).
MozReview-Commit-ID: BLPmCFNtzEl
--HG--
extra : rebase_source : 8ea4abbc8f8847a306d3bac4fd87d07e0ccb8f89
107889f3af