Reland change that speeds up multiple devices hot-reload (#23695)

* Revert "Revert "Run reload asynchronously so that multiple devices can reload in parallel. (#22693)" (#23598)"

This reverts commit 0b68068d6a33f35cec568ae6a9b394ff2a9fdb76.

* Fix refreshViews so it sends app-wide(rather than per-isolate) service request.

Sending per-isolate request caused dead-lock in the engine in case of more-than-one ui isolate.

packages/flutter_tools/lib/src/vmservice.dart

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index bc1586f..d248d3f 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart
@@ -949,15 +949,12 @@
     return invokeRpcRaw('_getVMTimeline', timeout: kLongRequestTimeout);
   }
 
-  Future<void> refreshViews() async {
+  Future<void> refreshViews() {
     if (!isFlutterEngine)
-      return;
+      return null;
     _viewCache.clear();
-    for (Isolate isolate in isolates.toList()) {
-      await vmService.vm.invokeRpc<ServiceObject>('_flutter.listViews',
-          timeout: kLongRequestTimeout,
-          params: <String, dynamic> {'isolateId': isolate.id});
-    }
+    // Send one per-application request that refreshes all views in the app.
+    return vmService.vm.invokeRpc<ServiceObject>('_flutter.listViews', timeout: kLongRequestTimeout);
   }
 
   Iterable<FlutterView> get views => _viewCache.values;
@@ -1226,15 +1223,15 @@
       Duration timeout,
       bool timeoutFatal = true,
     }
-  ) async {
-    try {
-      return await invokeRpcRaw(method, params: params, timeout: timeout, timeoutFatal: timeoutFatal);
-    } on rpc.RpcException catch (e) {
-      // If an application is not using the framework
-      if (e.code == rpc_error_code.METHOD_NOT_FOUND)
-        return null;
-      rethrow;
-    }
+  ) {
+    return invokeRpcRaw(method, params: params, timeout: timeout,
+        timeoutFatal: timeoutFatal).catchError((dynamic error) {
+            if (error is rpc.RpcException) {
+              // If an application is not using the framework
+              if (error.code == rpc_error_code.METHOD_NOT_FOUND)
+                return null;
+              throw error;
+            }});
   }
 
   // Debug dump extension methods.
@@ -1288,20 +1285,20 @@
   }
 
   // Reload related extension methods.
-  Future<Map<String, dynamic>> flutterReassemble() async {
-    return await invokeFlutterExtensionRpcRaw(
+  Future<Map<String, dynamic>> flutterReassemble() {
+    return invokeFlutterExtensionRpcRaw(
       'ext.flutter.reassemble',
       timeout: kShortRequestTimeout,
       timeoutFatal: true,
     );
   }
 
-  Future<Map<String, dynamic>> uiWindowScheduleFrame() async {
-    return await invokeFlutterExtensionRpcRaw('ext.ui.window.scheduleFrame');
+  Future<Map<String, dynamic>> uiWindowScheduleFrame() {
+    return invokeFlutterExtensionRpcRaw('ext.ui.window.scheduleFrame');
   }
 
-  Future<Map<String, dynamic>> flutterEvictAsset(String assetPath) async {
-    return await invokeFlutterExtensionRpcRaw('ext.flutter.evict',
+  Future<Map<String, dynamic>> flutterEvictAsset(String assetPath) {
+    return invokeFlutterExtensionRpcRaw('ext.flutter.evict',
       params: <String, dynamic>{
         'value': assetPath,
       }
@@ -1309,8 +1306,8 @@
   }
 
   // Application control extension methods.
-  Future<Map<String, dynamic>> flutterExit() async {
-    return await invokeFlutterExtensionRpcRaw(
+  Future<Map<String, dynamic>> flutterExit() {
+    return invokeFlutterExtensionRpcRaw(
       'ext.flutter.exit',
       timeout: const Duration(seconds: 2),
       timeoutFatal: false,