CL: https://codereview.chromium.org/2680113002/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/273c082d54d0403ca0b7fb65729cee7ff25473f0

commit 273c082d54d0403ca0b7fb65729cee7ff25473f0
Author: bruthig <bruthig@chromium.org>
Date: Wed Feb 08 22:34:01 2017

[ash-md] Remove non-md code from the Shelf background animations.

This change removes the asset based background used by pre-material
design shelf animations.

BUG= 687810 
TEST=ash_unittests

Review-Url: https://codereview.chromium.org/2680113002
Cr-Commit-Position: refs/heads/master@{#449111}

[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/overflow_bubble_view.cc
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_background_animator.cc
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_background_animator.h
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_background_animator_observer.h
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_background_animator_unittest.cc
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_constants.cc
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_constants.h
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/shelf/shelf_widget.cc
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/common/wm/dock/docked_window_layout_manager.cc
[modify] https://crrev.com/273c082d54d0403ca0b7fb65729cee7ff25473f0/ash/resources/ash_resources.grd
[delete] https://crrev.com/ce3f7a721ca8dabb1b13ba506d9980d60c5e02ac/ash/resources/default_100_percent/common/shelf/shelf_background.png
[delete] https://crrev.com/ce3f7a721ca8dabb1b13ba506d9980d60c5e02ac/ash/resources/default_100_percent/common/shelf/shelf_corner.png
[delete] https://crrev.com/ce3f7a721ca8dabb1b13ba506d9980d60c5e02ac/ash/resources/default_200_percent/common/shelf/shelf_background.png
[delete] https://crrev.com/ce3f7a721ca8dabb1b13ba506d9980d60c5e02ac/ash/resources/default_200_percent/common/shelf/shelf_corner.png