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This CL fixes error message:

    Error in response to networkingPrivate.getNetworks: TypeError: Cannot read
    property 'GUID' of null", source: chrome://oobe/oobe (0)

and clears default network if it disappears from the list of networks.

Bug: 793262
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ia72e650b73202de56b8ec842dbcee81f65366793
Reviewed-on: https://chromium-review.googlesource.com/822171
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524287}