[video_player] set message handler to nil on detach from engine

[cg021]

Description

Allow message handler to be set to nil when detachFromEngineForRegistrar is called in FLTVideoPlayerPlugin.m on iOS. Method call handlers are already set to null on Android when onDetachedFromEngine is called. This behavior was commented out as a temporary patch before setting message handlers to nil when detaching from a dying engine was allowed in the flutter engine. It should be reintroduced to the plugin since the fix is in the engine.

Related Issues

flutter/flutterfire_temporary#15, flutter/flutter#57151, flutter/engine#18428, #2759

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[blasten]

It doesn't look like 57151 landed on stable yet

[cg021]

So 2759 isn't an appropriate workaround? Since 57151 is on master but not stable, would conditionally setting the messageHandler to nil if not on stable work (i.e. calling flutter channel using NSTask and storing the active channel in an NSString to make this check)?

[ldelafuente]

do you know if 57151 is already on stable v1.20.2?

[dannyvalentesonos]

@gaaclarke Can this get in now?

[gaaclarke]

flutter/engine#18428 was brought over in this roll flutter/flutter@f64f6e2

So, it's on stable.

[gaaclarke]

Please rebase to resolve the conflicts, otherwise lgtm.

[Salakar]

LGTM, pending changelog/pubspec updates

[google-cla]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and then comment @googlebot I fixed it.. If the bot doesn't comment, it means it doesn't think anything has changed.

ℹ️ Googlers: Go here for more info.

[Salakar]

@googlebot I fixed it.

[google-cla]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and then comment @googlebot I fixed it.. If the bot doesn't comment, it means it doesn't think anything has changed.

ℹ️ Googlers: Go here for more info.

[Salakar]

@googlebot I consent.

[google-cla]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and then comment @googlebot I fixed it.. If the bot doesn't comment, it means it doesn't think anything has changed.

ℹ️ Googlers: Go here for more info.

[Salakar]

@cg021 I have a feeling your CLA is no longer valid - could you check?

[russellwheatley]

LGTM

[cyanglaz]

looks like @cg021's CLA is no longer valid. Can we close this PR and open another one with valid CLA?

cc @blasten