Repository: flutter
Issue: [google_maps_flutter] controller.getLatLng() returns randomly "LatLng(-90.0, -180.0)" inside onMapCreated
Labels: platform-ios,p: maps,package,has reproducible steps,P2,found in release: 1.21,found in release: 2.0,found in release: 2.3,team-ios,triaged-ios

<!-- Thank you for using Flutter!

     If you are looking for support, please check out our documentation
     or consider asking a question on Stack Overflow:
      * https://flutter.dev/
      * https://api.flutter.dev/
      * https://stackoverflow.com/questions/tagged/flutter?sort=frequent

     If you have found a bug or if our documentation doesn't have an answer
     to what you're looking for, then fill our the template below. Please read
     our guide to filing a bug first: https://flutter.dev/docs/resources/bug-reports
-->

## Steps to Reproduce
1. Run a flutter app with `google_maps_flutter:` as a dependency
2. Render a GoogleMap widget:
`GoogleMap(
            mapType: MapType.normal,
            initialCameraPosition: _deviceLocation,
            onMapCreated: _mapCreatedHandler,
),`
3. Try to get latitude and longitude based on the screen coordinates
`void _mapCreatedHandler(GoogleMapController controller) {
controller.getLatLng(
      ScreenCoordinate(
        x: 0,
        y: 0,
      ).then((coordinates) => print(coordinates));
}`

**Expected results:** Should always return the map coordinates needed

**Actual results:** Returns sometimes `LatLng(-90.0, -180.0)`, some other times the actual coordinates and completely random, I don't know is it's related to the fact that getLatLng() is an asynchronous function.

<details>
  <summary>Logs</summary>

    `No issues found! (ran in 5.0s)`

```

`[✓] Flutter (Channel dev, v1.18.0-8.0.pre, on Mac OS X 10.15.4 19E287, locale en-AR)
    • Flutter version 1.18.0-8.0.pre at /Users/magax/Documents/dev/Flutter/tools/flutter
    • Framework revision e0c63cd35e (12 days ago), 2020-04-23 22:29:01 -0400
    • Engine revision d2ec21221e
    • Dart version 2.9.0 (build 2.9.0-3.0.dev b0d35855d8)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /Users/magax/Library/Android/sdk
    • Platform android-29, build-tools 29.0.3
    • ANDROID_HOME = /Users/magax/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 11.4.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 11.4.1, Build version 11E503a
    • CocoaPods version 1.9.1

[✓] Android Studio (version 3.6)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 44.0.2
    • Dart plugin version 192.7761
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)

[✓] VS Code (version 1.44.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.9.1

[✓] Connected device (1 available)
    • Magax’s iPhone • cd482d10f1eef699e7dxea7d962a7126c19aa24c • ios • iOS 13.4`
```

```
```

</details>