Task Manager Should remember the most recently enabled columns.

Task Manager Should remember the most recently enabled columns.

This CL:
1- Makes adding and removing columns to the task manager a lot easier
and cleaner.
2- Stores/retrieves the columns visibility to/from the local state
prefs.
3- Stores/retrieves the sorted column and the sort order.

TBR=thestig@chromium.org
BUG=452521
TEST=browser_tests --gtest_filter=NewTaskManagerViewTest.*

Committed: https://crrev.com/4e16add803fbb0ed18413496d3fb4424fa4957c6
Cr-Commit-Position: refs/heads/master@{#346524}

Review URL: https://codereview.chromium.org/1320563002

Cr-Commit-Position: refs/heads/master@{#346734}
(cherry picked from commit 4780b87d1c25f68c39abc623199f3e71a477d32d)

Committed: https://chromium.googlesource.com/chromium/src/+/66147f68983ac39e559afc9b3776d3da8454c7d5

[afakhry, 2015-09-10 21:14:00]

Committed patchset #1 (id:1) manually as
66147f68983ac39e559afc9b3776d3da8454c7d5 (presubmit successful).

[Lei Zhang, 2015-09-10 21:16:45]

rs lgtm

Maybe prepend "Merge to M46: " so it's more obvious that this is a merge next
time.