user activity: Normalize the pathname from pprof and CWP data.

I noticed that lots of files have .. symbols in the pathname.

BUG=None
TEST=None

Change-Id: I7dbdc84b36b9496f2d8fa21ec4fafe0f1417f256
Reviewed-on: https://chrome-internal-review.googlesource.com/282197


Tested-by: Evelina Dumitrescu <evelinad@google.com>
Commit-Queue: Evelina Dumitrescu <evelinad@google.com>
Reviewed-by: George Burgess <gbiv@google.com>
Reviewed-by: Ting-Yuan Huang <laszio@google.com>
Reviewed-on: https://chromium-review.googlesource.com/435905


Commit-Ready: Luis Lozano <llozano@chromium.org>
Tested-by: Luis Lozano <llozano@chromium.org>
Reviewed-by: Luis Lozano <llozano@chromium.org>