Revert current time clamp on ended; clamp paused time instead.
Clamping the current time within Pipeline leads to a race
a race condition while using |renderer_ended_|. The problem
that code was added for can mostly be fixed by instead clamping
the pause time in WebMediaPlayerImpl.
I've verified the HTMLMediaElement cleanup in another CL still
passes all tests: https://codereview.chromium.org/
456343002/
BUG=446637
TEST=layout tests, unittests.
Review URL: https://codereview.chromium.org/
843863002
Cr-Commit-Position: refs/heads/master@{#310686}