Provide executor getter for ExecutorLoopController

Summary: This change enables to acquire the executor from the current FiberManager when using ExecutorLoopController (which is already possible to do with the EventBase's loop controller).

Reviewed By: andriigrynenko

Differential Revision: D14515799

fbshipit-source-id: 3b9e48450bf58ea94bebab50dbbcfd7720f90d61

folly/fibers/ExecutorLoopController.h

@@ -33,6 +33,10 @@ class ExecutorLoopController : public fibers::LoopController {
   explicit ExecutorLoopController(folly::Executor* executor);
   ~ExecutorLoopController() override;
 
+  folly::Executor* executor() const {
+    return executor_;
+  }
+
  private:
   folly::Executor* executor_;
   Executor::KeepAlive<> executorKeepAlive_;