user activity: Added group extra CWP functions functionality.

Write the data of the functions that belong to a group in a CSV file,
sorted by their inclusive count value, in descendant order.

Create a CSV file containing the name of the groups, their common path,
the total inclusive count value of all the functions declared in files
that share the common path, sorted in descendant order by the inclusive
count value.

BUG=None
TEST=process_hot_functions_unittest passes

Change-Id: Ie0fe406ec0fefed02a5547dffa02e650dddd783a
Reviewed-on: https://chrome-internal-review.googlesource.com/282198


Reviewed-by: George Burgess <gbiv@google.com>
Reviewed-by: Ting-Yuan Huang <laszio@google.com>
Tested-by: Evelina Dumitrescu <evelinad@google.com>
Commit-Queue: Evelina Dumitrescu <evelinad@google.com>
Reviewed-on: https://chromium-review.googlesource.com/435904


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