auto-fetch: store tab ID in ClientId

This changes how the ClientId is generated for this feature. The tabID
is not used yet, but will be
needed to implement the system notification correctly.

I manually verified that FindTab() returns the correct ID.

Bug: 883486
Change-Id: I466fc5d3eb1b6f373d969a3d8eb88de7e96854ce
Reviewed-on: https://chromium-review.googlesource.com/c/1327409
Commit-Queue: Dan H <harringtond@google.com>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608057}
8 files changed