Created a chromium side bug for tracking.
Derek suggests that "we dynamically adjust the ping timeout value (known as livenessTimeout) based on past behavior. If a channel previously errored out due to ping_timeout, then the livenessTimeout value is bumped up slightly the next time we re-create the channel. This will help in cases where the ping messages takes a longer time to return by not prematurely closing the channel."
ref: b/37511031
Comment 1 by zhaobin@chromium.org
, Sep 22 2017