[google_maps_flutter] add zoom controls property

[ened]

Description

The Google Maps SDK on Android support the display of zoom control buttons in the bottom right (https://developers.google.com/maps/documentation/android-sdk/controls#zoom_controls).

The iOS SDK does NOT support this feature, at the moment.

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.

An existing test does not pass currently, this was introduced in #1953. Will include the fix in this PR.

Breaking Change

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

• No, this is not a breaking change.

[amirh]

@ened This is great, thanks! We would like to wait until we have maps implemented on both iOS and Android before actually further augmenting the API, because we are worried that they'll get out of sync otherwise (the current iOS implementation is temporarily dead code, remains of the overlay based plugin). Would you be ok with resubmitting in a few weeks once we have the iOS work more fleshed out?

[ened]

@amirh yes of course no problem. How could I help with the iOS port? Does it have blockers in the main project or engine?

[ened]

@amirh now updated as the iOS port has landed.

[timtraversy]

Are you using the latest clang-format? You need to bump to at least clang 7 on your machine, then run pub global run flutter_plugin_tools format --plugins google_maps_flutter. I ran into this issue while submitting a PR a few days ago.

[iskakaushik]

Hi @ened , thanks for the PR, could you please rebase?

[ened]

Ok will do today.

[ened]

@cyanglaz have updated this once again and reverted the manual setter method. It would force the GoogleMap class to loose it's const modifier and I believe we don't want that tradeoff for a simple assertion.
I have extended the documentation a bit to clarify the bits. I think it's clear enough from a dev-user point of view. WDYT?

[cyanglaz]

LGTM, please rebase and also implement the assertion on iOS for the setter.

[ened]

Thank you for reviewing again @cyanglaz. Are you absolutely sure that a assertion is necessary on iOS.

Even a non-setter method assertion like this:

assert(zoomControlsEnabled == true && Platform.isIOS,
            'Property is not supported on iOS'),

Will cause GoogleMap to loose the const qualifier (as Platform isn't const).

[cyanglaz]

Let's change this to: This is only supported on Android. And this field is silently ignored on iOS.

[cyanglaz]

Thank you for reviewing again @cyanglaz. Are you absolutely sure that a assertion is necessary on iOS.

Even a non-setter method assertion like this:

assert(zoomControlsEnabled == true && Platform.isIOS,
            'Property is not supported on iOS'),

Will cause GoogleMap to loose the const qualifier (as Platform isn't const).

I see. Let's keep it as an no-op but update the doc to be clearer.
Please rebase the PR and we can land this :)

[ened]

Done. Additionally, not having the assertion also makes the client code a lot easier.

Else I'd have to if/else wrap the zoomControls setter to null on iOS and the actual value on Android for example.

Will land once green..

[cyanglaz]

@ened It seems the PR is out of date. Would you be able to work on it and resolve conflicts?

[ened]

@cyanglaz done