GitLab

Introduce a Live Caption toggle image button in the volume slider. This
UI follows the Android pattern of offering a Live Caption button in the
volume controls, enabling easy access to toggle the feature on and off.

This CL does a few things:
1. Moves the live_caption icon from chrome/app/vector_icons to
components/vector_icons so that it can be shared with chrome and ash,
and renames it as live_caption_on.
2. Introduces a new icon, live_caption_off.
3. Introduces a LiveCaptionButton in the UnifiedVolumeView.
4. Since the new LiveCaptionButton shares code with the MoreButton,
introduces a new template, UnifiedVolumeViewButton, which contains the
shared ink drop and color code.
5. Defines the kLiveCaptionEnabled pref name in ash (synced with the
chrome pref).
6. Introduces a new toggle_background to the ToggleImageButton which
allows buttons to toggle their background color when the toggled state
changes.

Screenshots:
Live Caption off: https://screenshot.googleplex.com/BRoxxFsssg9f6ix
Live Caption on: https://screenshot.googleplex.com/58TfboB96UU273Z

Bug: 1055150, 1111002
AX-Relnotes: N/A (feature has not launched yet)
Change-Id: Ie8b3736eaee3a2fc4ba841de8d98dd8c95495e95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2571481Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Commit-Queue: Abigail Klein <abigailbklein@google.com>
Cr-Commit-Position: refs/heads/master@{#833763}