Add missing using statement in notify_server_test.cc.
Add missing using statement in notify_server_test.cc.

The test currently compile because of ADL (argument-dependent lookup). It
does not compile with a more recent googletest version. See associated
bug for linked to failed builds and compiler error messages.

Bug: crashpad:274
Change-Id: I7f2dd736453deb2a1af7bcacefc421961e1eb95e
Reviewed-on: https://chromium-review.googlesource.com/c/1422786
Commit-Queue: Victor Costan <f9d74ff10d707bcbd53fd3136f6e305255776c7a@chromium.org>
Reviewed-by: Scott Graham <e134406e1863f3b48b0795831afac5c0595efb36@chromium.org>

chromium/crashpad,chromium/crashpad,chromium/crashpad