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This CL does the following:
1) If we choose a tool that is a "mode", the palette tray stays active.
2) If a tool that is a "mode" is active, tapping the palette tray deactives the tool.
3) Remove the checkmarks (because they can't be seen anymore with #2).
4) Add a seperator between tools that are "actions" and tools that are "modes".

Test: ash_unittests --gtest_filter="PaletteTrayTest.*"
Bug: 742524
Change-Id: I70d6e07a460250e7a22059973de036146dd753a6
Reviewed-on: https://chromium-review.googlesource.com/572066
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488108}