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This CL creates javatests target in signin.ui module and moves confirm
sync data integration tests to the target.

Bug: 1158307
Change-Id: If139ed6453f41189d49ff5640d3f7bfcb91c88e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587733Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837009}