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Copy the tab switching benchmark to cros_benchmarks. Using key events for
simulate tab switching behavior to handle the case that some tab contexts
may be discarded.

Example usage to open 120 tabs:
$ ./run_benchmark --browser=cros-chrome --remote=DUT_IP
cros_tab_switching.typical_24 --tabset-repeat=5

BUG=724381

Review-Url: https://codereview.chromium.org/2890333002
Cr-Commit-Position: refs/heads/master@{#474975}