Add real PluginVm launcher icon image.

This commit replaces the temporary PluginVm launcher icon image with an
image from the design team.
The helper function that controls the visibility of the icon still always
returns false, so the icon will never be visible. Visibility will be
linked to enterprise policies in another CL.

Bug: 904847
Test: none
Change-Id: Ie3b7869edd7093222b2b1fd3a4a9bba7880de7a7
Reviewed-on: https://chromium-review.googlesource.com/c/1397609
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Alex Oldemeier <aoldemeier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620768}