Partially remove dependency on folly async

Summary:
This change isolates the usage of folly async from Flipper. Is now self-contained in Flipper Folly schedulers.

Users of Flipper can decide not to use the types defined in that header and implement their own.

NOTE: changes are minimal, we are just replacing direct calls to folly event base with a scheduler which simply relays this on to folly.

Reviewed By: fabiomassimo

Differential Revision: D36626483

fbshipit-source-id: add0241caf4af0aa5c3b5c2e7efc2e725f5400ab

xplat/Flipper/FlipperSocketProvider.h

@@ -7,8 +7,8 @@
 
 #pragma once
 
-#include <folly/io/async/EventBase.h>
 #include <memory>
+#include "FlipperScheduler.h"
 
 namespace facebook {
 namespace flipper {
@@ -32,35 +32,37 @@ class FlipperSocketProvider {
    @param endpoint Endpoint to connect to.
    @param payload Any configuration payload to establish a connection with
    the specified endpoint.
-   @param eventBase A folly event base used to execute connection operations.
+   @param scheduler An scheduler used to schedule and execute connection
+   operations.
    */
   virtual std::unique_ptr<FlipperSocket> create(
       FlipperConnectionEndpoint endpoint,
       std::unique_ptr<FlipperSocketBasePayload> payload,
-      folly::EventBase* eventBase) = 0;
+      Scheduler* scheduler) = 0;
   /**
    Create an instance of FlipperSocket.
    @param endpoint Endpoint to connect to.
    @param payload Any configuration payload to establish a connection with
    the specified endpoint.
-   @param eventBase A folly event base used to execute connection operations.
+   @param scheduler An scheduler used to schedule and execute connection
+   operations.
    @param connectionContextStore A connection context store used for obtaining
    the certificate used for secure connections.
    */
   virtual std::unique_ptr<FlipperSocket> create(
       FlipperConnectionEndpoint endpoint,
       std::unique_ptr<FlipperSocketBasePayload> payload,
-      folly::EventBase* eventBase,
+      Scheduler* scheduler,
       ConnectionContextStore* connectionContextStore) = 0;
 
   static std::unique_ptr<FlipperSocket> socketCreate(
       FlipperConnectionEndpoint endpoint,
       std::unique_ptr<FlipperSocketBasePayload> payload,
-      folly::EventBase* eventBase);
+      Scheduler* scheduler);
   static std::unique_ptr<FlipperSocket> socketCreate(
       FlipperConnectionEndpoint endpoint,
       std::unique_ptr<FlipperSocketBasePayload> payload,
-      folly::EventBase* eventBase,
+      Scheduler* scheduler,
       ConnectionContextStore* connectionContextStore);
 
   static void setDefaultProvider(