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This CL:
1. Does not initialize the network cache until the user's networks
have been loaded.
2. Queues calls to GetAllSyncableNetworks until the network cache
has been loaded

Bug: 1154341
Change-Id: I158cb29109c9f8de52ff09f1c82866931e371459
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2600119
Commit-Queue: Claude van der Merwe <cvandermerwe@google.com>
Reviewed-by: Azeem Arshad <azeemarshad@chromium.org>
Reviewed-by: Jon Mann <jonmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841610}