Modified LocalDiscoveryUIBrowsertest to use actual ServiceDiscoveryClientImpl

Removed mock PrivetDeviceLister, changed LocalDiscoveryUIBrowsertest to use a
testing ServiceDiscoverySharedClient that delegates to a
ServiceDiscoveryClientImpl with a mocked network, allowing the test to be
written in terms of packets rather than calls to method of PrivetDeviceLister.

BUG=

Review URL: https://codereview.chromium.org/25649002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227197 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227197