Improve TextTrack/TextTrackCue exception messages.

BUG=270033

Review URL: https://codereview.chromium.org/80523002

git-svn-id: svn://svn.chromium.org/blink/trunk@162528 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Improve TimeRanges exception messages.

BUG=270033

Review URL: https://codereview.chromium.org/80633003

git-svn-id: svn://svn.chromium.org/blink/trunk@162529 bbb929c8-8fbe-4397-9dbb-9b2b20218538