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In this cl, we are trying to add the logcat of each instrumentation
test into the corresponding test result object, so that when we are
checking the result of each test case, we would be able to see the
corresponding logcat for that test case at the same time.

BUG=631213

Review-Url: https://codereview.chromium.org/2451523002
Cr-Commit-Position: refs/heads/master@{#435041}