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Non-blocking IO has higher throughput than the previous implementation
that used overlapped IO. 15% increase in throughput for sending to
localhost is observed. There could be additional performance advantage
in WiFi network.

All existing UDP socket tests passed. I added a unit test to do
benchmarking. Also tested this manually with WebRTC and verified that
all UDP send and receive activities are logged correctly.

BUG=442392

Review URL: https://codereview.chromium.org/861963002

Cr-Commit-Position: refs/heads/master@{#314752}