[url_launcher_web] Regenerate mocks used by integration tests.

[ditman]

Mocks in the integration_tests of url_launcher_web have started failing to compile with the following error:

org-dartlang-app:/url_launcher_web_test.mocks.dart:585:12: Error: Type '_i2.DatabaseCallback' not found.
          [_i2.DatabaseCallback? creationCallback]) =>
           ^^^^^^^^^^^^^^^^^^^^
org-dartlang-app:/url_launcher_web_test.mocks.dart:585:16: Error: 'DatabaseCallback' isn't a type.
          [_i2.DatabaseCallback? creationCallback]) =>
               ^^^^^^^^^^^^^^^^

See: https://cirrus-ci.com/task/5677093640994816?logs=drive#L714

Possibly caused by this change in dart:html.

This PR regenerates the mocks using the latest tip from flutter/master + the latest mockito version.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed 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.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

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[gaaclarke]

lgtm!

[ditman]

Merged into #4451 so @gaaclarke can cleanly land his PR and unblock the tree.