Install Extension from portal fails with InvalidOperationException

POST admin/host/extensions fails with the below exception.

CRI 92958585

FunctionsLogs
| where Tenant == "6d56b41487174733b7d25ec070fc19d7"
| where TIMESTAMP >= datetime(2018-11-17 16:10:00) and TIMESTAMP <= datetime(2018-11-20 23:10:00)
| where ActivityId contains "a4700371-f6f5-4b6d-aea1-02a2f71e94dc" or Details contains "BindingExtensions"
| where HostVersion == "2.0.12180.0"
| where RoleInstance == "SmallDedicatedWebWorkerRole_IN_22"

System.InvalidOperationException : Unable to resolve service for type 'Microsoft.Azure.WebJobs.Script.BindingExtensions.IExtensionsManager' while attempting to activate 'Microsoft.Azure.WebJobs.Script.WebHost.Controllers.ExtensionsController'.
at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp,Type type,Type requiredBy,Boolean isDefaultParameterRequired)
at lambda_method(Closure ,IServiceProvider ,Object[] )
at Microsoft.AspNetCore.Mvc.Controllers.ControllerActivatorProvider.<>c__DisplayClass4_0.b__0(ControllerContext controllerContext)
at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass5_0.g__CreateController|0(ControllerContext controllerContext)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next,Scope& scope,Object& state,Boolean& isCompleted)
at async Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeInnerFilterAsync()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeNextResourceFilter()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResourceExecutedContext context)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next,Scope& scope,Object& state,Boolean& isCompleted)
at async Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeFilterPipelineAsync()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeAsync()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.WebHost.Middleware.FunctionInvocationMiddleware.Invoke(HttpContext context) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\Middleware\FunctionInvocationMiddleware.cs : 49
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.WebHost.Middleware.HomepageMiddleware.Invoke(HttpContext context) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\Middleware\HomepageMiddleware.cs : 34
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.AspNetCore.Buffering.ResponseBufferingMiddleware.Invoke(HttpContext httpContext)
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.WebHost.Middleware.ExceptionMiddleware.Invoke(HttpContext context) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\Middleware\ExceptionMiddleware.cs : 28

Start with the Microsoft.Azure.WebJobs.Script.WebHost.Controllers.ExtensionsController entry point and the dependency-injection registration for IExtensionsManager. Reproduce POST admin/host/extensions using the reported failure context, then verify the request no longer raises InvalidOperationException.

Written by the indexing model from the issue text.