[cross_file] Use Blobs to store files on the web. (flutter#494)

[pigeon] added support for explicit objects (flutter#483)

[flutter_markdown] Padding builder (flutter#486)

[animations] Updated open_container.dart documentation. (flutter#499)

[palette_generator] Fix typos (flutter#487)

[flutter_markdown] add padding for p, h1-h6 (flutter#465)

[rfw] Update docs and coverage (flutter#480)

Apply review comments from Yegor (flutter#474)

[pigeon] fixed nested classes type arguments can be omitted from the …

…output (flutter#471)

[extension_google_sign_in_as_googleapis_auth] Update example app. (fl…

…utter#466)

* Regenerate example app with:
    ```
    flutter create googlesigninexample --org io.flutter.plugins --ios-language=objc --android-language=java
    ```
* Prepare the google sign in integration, and bring the latest code from lib/main.dart of the google_sign_in package.
* Apply code changes to use the extension package.