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Add UMA metrics to connectivity detector.
Also, add some adb logging to make it easier to understand the
functionality of connectivity detector.
Finally, prevent the retry delay from overlflowing.

Change-Id: I3de32e01c20aeef04648685bb074012618e73831
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514065
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Jian Li <jianli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828347}