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This CL implements DetailedViewController for the network detailed view.
The change is a step to remove the reference to SystemTray from
UnifiedSystemTray. It fixes the behavior of the back button, and enables
further UnifiedSysetmTray specific tweaks to the detailed view.

To implement the common behavior for UnifiedSystemTray detailed views,
this CL also adds UnifiedDetailedViewDelegate.

TEST=manual
BUG=835733

Change-Id: I2c005db58e410d33a36e6b6e16083b30917bc053
Reviewed-on: https://chromium-review.googlesource.com/1071490Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561798}