Expose APIs for updating a list of CRX components

[antonok-edm]

During development of brave/brave-core#21868, it was determined that Chromium doesn't expose any APIs for updating a set of CRX components in a single request.

As described in brave/brave-core#21868 (comment), we want to have something like CrxUpdateService::OnDemandUpdateMultipleIds. We'll need the ability to change priority between BACKGROUND and FOREGROUND, as well: these APIs will be used both for user-initiated update checks (e.g. brave/brave-core#22881) and automatic background update checks.

[diracdeltas]

is this just for updating our internal crx's? if it can be used to update user-installed extensions then that's a fingerprinting risk since it can be unique.

[ShivanKaul]

The intention was only Brave-pushed components.

[mherrmann]

it was determined that Chromium doesn't expose any APIs for updating a set of CRX components in a single request.

I'm not sure if there's a difference between on-demand and background updates. But the last time I worked with the code, upstream absolutely did have an API for updating multiple components in the background with a single request. See SequentialUpdateChecker in our code. Maybe it's different for on-demand updates.

[mherrmann]

@goodov mentioned here now that upstream has APIs for batch updates for background update checks, but not for on-demand update checks. However, we disable batching with a class called SequentialUpdateChecker. I implemented this some years ago and explained the reasoning in comments in the source code.

I wonder if we really need batch update checks for on-demand updates. And maybe we can find an alternative to the SequentialUpdateChecker solution that gives us batch update checks for background updates. I outline such an alternative in brave/brave-core#23169 (review).