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Add CastDialogMetrics, which will be used by CastDialogView to
record various UI metrics. The recorder will keep track of when/if
certain events (init, paint, load sinks, first user action) happened,
to record when an event happens for the first time, and the durations
between events.

MediaRouterMetrics calls that CastDialogView was making directly will
now go through CastDialogMetrics.

Metrics recorded by CastDialogMetrics via MediaRouterMetrics:
MediaRouter.Ui.Device.Count
MediaRouter.Ui.Dialog.Paint
MediaRouter.Ui.Dialog.LoadedWithData (new)
MediaRouter.Ui.Action.StartLocalPosition
MediaRouter.Ui.Action.CloseLatency (new)
MediaRouter.Ui.Action.StartLocal.Latency (new)
(MediaRouter.Ui.FirstAction will be added later)
(MediaRouter.Ui.Action.StopRoute will be added later)

Bug: 853369
Change-Id: Ib27ecc9293fd148d8592b76b22c9fbab3910a5e5
Reviewed-on: https://chromium-review.googlesource.com/1135582
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575129}