Speed up Flipper by using background queue for serialization

Reviewed By: jknoxville

Differential Revision: D21290732

fbshipit-source-id: 21fcb793900a6517d764fa3a581255fd75a39801

iOS/Plugins/FlipperKitLayoutPlugin/SonarKitLayoutPluginTests/SonarKitLayoutPluginTests.m

@@ -67,6 +67,11 @@
   SonarReceiver receiver = connection.receivers[@"getNodes"];
   receiver(@{@"ids" : @[]}, responder);
 
+  dispatch_barrier_sync(
+      SKLayoutPluginSerialBackgroundQueue(),
+      ^{
+      });
+
   XCTAssertTrue(([responder.successes containsObject:@{@"elements" : @[]}]));
 }
 
@@ -96,6 +101,11 @@
   receiver(
       @{@"ids" : @[ @"testNode1", @"testNode2", @"testNode3" ]}, responder);
 
+  dispatch_barrier_sync(
+      SKLayoutPluginSerialBackgroundQueue(),
+      ^{
+      });
+
   XCTAssertTrue(([responder.successes containsObject:@{
     @"elements" : @[
       @{
@@ -149,6 +159,11 @@
   SonarReceiver getNodesCall = connection.receivers[@"getNodes"];
   getNodesCall(@{@"ids" : @[ @"testNode1", @"testNode2" ]}, responder);
 
+  dispatch_barrier_sync(
+      SKLayoutPluginSerialBackgroundQueue(),
+      ^{
+      });
+
   SonarReceiver setHighlighted = connection.receivers[@"setHighlighted"];
   setHighlighted(@{@"id" : @"testNode2"}, responder);
 
@@ -249,6 +264,11 @@
   connection.receivers[@"getRoot"](@{}, responder);
   connection.receivers[@"getNodes"](@{@"ids" : @[ @"testNode2" ]}, responder);
 
+  dispatch_barrier_sync(
+      SKLayoutPluginSerialBackgroundQueue(),
+      ^{
+      });
+
   // Modify the name of testNode3
   connection.receivers[@"setData"](
       @{