Disable progressive playback support by default

[osagie98]

Implements a BASE_FEATURE for Cobalt progressive playback support and disables it by default. Progressive playback can be enabled at runtime by passing the argument "--enable-features=CobaltProgressivePlayback". This change only affects Cobalt Starboard Media builds.

b/382791540

[yell0wd0g]

This should add a unit test (to third_party/blink/renderer/core/html/media/html_media_element_test.cc), it shouldn't be too hard.

The function in base/test/scoped_feature_list.h can help for enabling base::Features safely for testing.

[osagie98]

This should add a unit test (to third_party/blink/renderer/core/html/media/html_media_element_test.cc), it shouldn't be too hard.

The function in base/test/scoped_feature_list.h can help for enabling base::Features safely for testing.

@yell0wd0g I commented elsewhere in this PR:

I've removed the test to unblock this (it crashes on Android). The test is saved, and once we validate blink tests on Android I'll re-add it.

[yell0wd0g]

This should add a unit test (to third_party/blink/renderer/core/html/media/html_media_element_test.cc), it shouldn't be too hard.
The function in base/test/scoped_feature_list.h can help for enabling base::Features safely for testing.

@yell0wd0g I commented elsewhere in this PR:

I've removed the test to unblock this (it crashes on Android). The test is saved, and once we validate blink tests on Android I'll re-add it.

If you can compile and run it on Linux, I'd say add it, since anyway blink_unittest APK is not ran anywhere, so it wouldn't crash : )
It's best to land the unit test with the code itself, for history purposes for example (cherry-picking etc).

[yell0wd0g]

Looking good but I'd add the unit test anyhow and also try and make const any variable that can be const.

[yell0wd0g]

LGTM! Thanks for bringing the unit tests!

[osagie98]

Merge pending discussion if we want to start with C25 only: #4564

[xiaomings]

Just to double check if this can handle queries without space after ',', e.g. 'video/mp4; codecs="avc1.42001E,mp4a.40.2"', which are also valid.

Since we are not checking the exact value, splitting on ',' can handle cases with or without extra space. In either case, we should comment here mentioning that this is not comprehensive.

Also, is this function called by the H5 player with a single codec?

[osagie98]

Created a new PR #4624 that strips whitespace.

Now that progressive is disabled, this function will be called on single codec formats as well. There may be a performance hit that I haven't analyzed.