Add test for starting a bubble session when one is active

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Please feel free to make changes to the generated tests based on your domain knowledge. More context about the project please see go/ai-testgen

Original Change: ag/35390097 (Note tests are based on the original CL but may add coverage beyond the specific changes to improve overall code health)

Test: ATP tests passed http://go/forrest-run/L40600030017639478
Bug: 431235865
Flag: TEST_ONLY



Change-Id: Id57f7a429a6f7547bcec0d5fe88e51ad25e9c4e3