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This change does two things.  First, it splits out the implementation
of ServiceDiscoveryDeviceLister from the interface, which will allow
users of the API to mock/fake it for testing.

Second, it adds a service_type parameter to
ServiceDiscoveryDeviceLister::Delegate::OnDeviceCacheFlushed.  This
allows users of the class that want to manage multiple service types
with a single Delegate to disambiguate which service is being flushed.
The other Delegate functions already pass in the service description
so don't need any additional information for this use.

Also fixup callsites for all users of this API.

Bug: 808157
Change-Id: I9cf4b23692f54c66e0224e06df1769f750f846b3
Reviewed-on: https://chromium-review.googlesource.com/898184
Commit-Queue: Justin Carlson <justincarlson@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Gene Gutnik <gene@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534146}