This is not used anywhere in the engine. However, this API is easy to misuse as
one might incorrectly assume that it releases the reference on the underlying
object. Callers must use `reset` for this purpose.

* Remove unnecessary `?`s from web_ui.

In https://dart-review.googlesource.com/c/sdk/+/163841, dart's flow
analysis is being changed so that an assignment like this:

    T? x = <non-nullable value>;

causes `x` to be immediately promoted to type `T`.  This exposed two
instances in which a variable was unnecessarily given a nullable type.
To avoid warnings, we need to fix these two types before
https://dart-review.googlesource.com/c/sdk/+/163841 can land.

* Reland "Apply dpr transform to fuchsia accessibility bridge (#21364)"

This reverts commit 9db9a57a.

* fix test

This reverts commits
- 67fdd7ed.
- 854943d5.

See: https://github.com/flutter/flutter/issues/66829

This reverts commit cf1fbf27.

* Apply dpr transform to fuchsia accessibility bridge

* fix format

* addressing comment

* fix typo

https://dart.googlesource.com/sdk.git/+log/200e8da5072a..c938793e2d6f

2020-09-26 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.11.0-169.0.dev

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