GitLab

Many ClientSession unittests assume that the first video frame always
contains video dimensions. When running under valgrind the keep-alive timer
may fire before the first video frame is sent and this breaks the tests.

Fixed VideoFramePump to start sending keep-alive messages only after the
first real frame is sent. Also made the keep-alive timer non-repeating.
This ensures that the pump doesn't try sending a keep-alive message until
the previous one has been sent.

BUG=458691

Review URL: https://codereview.chromium.org/936553003

Cr-Commit-Position: refs/heads/master@{#316933}