[webview_flutter] Disable legacy Android video poster

[lauweijie]

It looks like the chromium team is considering disabling the default video poster feature: https://issues.chromium.org/issues/40755557. This changes it to an empty bitmap for now.

Fixes flutter/flutter#178263.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

Note: The Flutter team is currently trialing the use of Gemini Code Assist for GitHub. Comments from the gemini-code-assist bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

[gemini-code-assist]

Code Review

This pull request disables the legacy Android video poster image by overriding WebChromeClient.getDefaultVideoPoster to return a minimal transparent bitmap. This prevents the default gray play icon from showing on videos before they start. The change is accompanied by a new unit test and a changelog update. My review focuses on the correctness of the implementation and the quality of the test. I have one suggestion to make the new test more specific and robust.

[bparrishMines]

Opted out to land in downstream fork for now.

[fluttergithubbot]

An existing Git SHA, ab5b85c8b01177f3673950a056c7f188b116b505, was detected, and no actions were taken.

To re-trigger presubmits after closing or re-opeing a PR, or pushing a HEAD commit (i.e. with --force) that already was pushed before, push a blank commit (git commit --allow-empty -m "Trigger Build") or rebase to continue.

[reidbaker]

@lauweijie is this ready for review or did you want it to be a draft?

[bparrishMines]

@reidbaker I set this as a draft while we wait to see what the process will be to roll this plugin internally. It's only open still to ensure that we revisit it after a decision. But I'm also open to closing it for now if it is easier for triage teams.

[reidbaker]

I just wanted to make sure that it wasn't accidentally marked as draft.