Add isMethodSupported handler

Summary: Allows plugin to check if something is supported by that app, for example an extension command or a new feature, before trying to use it.

Reviewed By: passy

Differential Revision: D14225957

fbshipit-source-id: 3c5a29a06b56fe5f1da772824232547447872344

xplat/Flipper/FlipperConnectionImpl.h

@@ -53,6 +53,13 @@ class FlipperConnectionImpl : public FlipperConnection {
     receivers_[method] = receiver;
   }
 
+  /**
+  Runtime check which receivers are supported for this app
+  */
+  bool hasReceiver(const std::string& method) {
+    return receivers_.find(method) != receivers_.end();
+  }
+
  private:
   FlipperConnectionManager* socket_;
   std::string name_;