onBraveThemeTypeChanged not getting called from extension page

[petemill]

Here is a branch that is attempting to use chrome.braveTheme.onBraveThemeTypeChanged event handler:
brave/brave-core@try-shields-theme...try-shields-theme-onchange edit: now on master

It is not getting fired when the system theme is changed.

Steps to reproduce

• Run the above branch
• In Settings, change theme to 'Same as macOS'
• Visit a website
• Open shields panel
• Keep shields panel open and change macOS theme
  Observed: theme doesn't change
  Expected: theme changes

This is not a huge issue for Shields panel, but is a nice to have, especially for other webui.

Assigning to 0.63.x for now since 'Same as macOS' was introduced there, but this is not urgent.

[simonhong]

I found that current implementation only fires onBraveThemeTypeChanged when preference is changed. I missed this 👍

[petemill]

Uplifting only to 0.64.x as the only code that depends on this event is in 0.64.x

[LaurenWags]

@petemill @simonhong is this one macOS (specifically Mojave) only?

[simonhong]

@LaurenWags extension page on Windows should be also changed by windows os theme change. Howeve, another PR was needed for Windows and only nightly will work properly.
For dev, beta, uplift PRs are waiting for approving. brave/brave-core#2332 and brave/brave-core#2331.

[btlechowski]

Based on the above comment, added OS/macOS label

[simonhong]

@btlechowski yes, it's correct 👍

[LaurenWags]

@kjozwiak can you check this one since you have Mojave?

[kjozwiak]

Verification PASSED on macOS 10.14.4 x64 using the following build:

Brave	0.64.72 Chromium: 74.0.3729.131 (Official Build) beta(64-bit)
Revision	518a41c1fa7ce1c8bb5e22346e82e42b4d76a96f-refs/branch-heads/3729@{#954}
OS	Mac OS X

• Went through the original test case outlined under onBraveThemeTypeChanged not getting called from extension page #3882 (comment)