Unable to switch build platform after selecting facebook in Build Settings.
Gameroom option is missing in build settings for Facebook platform.

Steps to repro:
1. Create a new Project.
2. File > Build Settings
3. Select the Facebook Platform.

Actual result:
Unable to switch build platform after selecting facebook in Build Settings.
NullReferenceException is thrown in console.

Expected Result:
The platform should be switched in build settings.

Reproducible in:
2019.1.0a11.

Working Fine in:
2019.1.0a10, 2019.1.0a1, 2018.3.0f1.

Environment:
Windows & Mac.

Stack trace:
NullReferenceException: Object reference not set to an instance of an objectUnityEditor.BuildPlayerWindow.ShowBuildTargetSettings () (at C:/buildslave/unity/build/Editor/Mono/BuildPlayerWindow.cs:685)UnityEditor.BuildPlayerWindow.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/BuildPlayerWindow.cs:367)System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:357)UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:351)UnityEditor.HostView.OldOnGUI () (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:147)UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, Matrix4x4 parentTransform, Rect clippingRect, Boolean isComputingLayout) (at C:/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:246)UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)