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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}