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This CL embeds old SystemTray's detailed views to UnifiedSystemTray.
Although this is temporary, this feature is important to start
early dogfooding, and requested multiple times from PM.
When we launch the feature, SystemTray instance is completely removed,
so this temporary hack will not work. Before launch, we're going to
replace all of them with our own implementation of detailed views.

TEST=manual
BUG=835733

Change-Id: Ic94f3ffa1976e3812f6bf200b64f1ec03878715c
Reviewed-on: https://chromium-review.googlesource.com/1023354Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553435}