The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eafc7f07429efa84bbb3e5b8f3a8f3e8a3ada0d5

commit eafc7f07429efa84bbb3e5b8f3a8f3e8a3ada0d5
Author: Sriram <srirama.m@samsung.com>
Date: Mon Nov 20 06:55:29 2017

[WebVTT] Update dom construction logic for timestamp per spec

According to the spec [1] we need to include optional components
and add leading zeros if required for timestamp construction.
[1]: https://w3c.github.io/webvtt/#dom-construction-rules

Bug:  786382 
Change-Id: I2b7320bd6b187cb3b85a5532c0a0fd398b3888cf
Reviewed-on: https://chromium-review.googlesource.com/773763
Commit-Queue: srirama chandra sekhar <srirama.m@samsung.com>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#517767}
[modify] https://crrev.com/eafc7f07429efa84bbb3e5b8f3a8f3e8a3ada0d5/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/getCueAsHTML-expected.txt
[delete] https://crrev.com/965bbf35c6645b47427b236cf49d696faf7d306a/third_party/WebKit/LayoutTests/external/wpt/webvtt/parsing/cue-text-parsing/tests/timestamps-expected.txt
[delete] https://crrev.com/965bbf35c6645b47427b236cf49d696faf7d306a/third_party/WebKit/LayoutTests/media/track/opera/track/webvtt/parsing-cue-data/tests/timestamps-expected.txt
[modify] https://crrev.com/eafc7f07429efa84bbb3e5b8f3a8f3e8a3ada0d5/third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp