Use signature inheritance when method types are unchanged

lib/runtime/dart/isolate.js

 var isolate = dart.defineLibrary(isolate, {});
 var core = dart.import(core);
 var _isolate_helper = dart.lazyImport(_isolate_helper);
 var async = dart.import(async);
 (function(exports, core, _isolate_helper, async) {
   'use strict';
   class Capability extends core.Object {
     Capability() {
       return new _isolate_helper.CapabilityImpl();
     }
   }
   dart.setSignature(Capability, {});
   class IsolateSpawnException extends core.Object {
     IsolateSpawnException(message) {
       this.message = message;
     }
     toString() {
       return `IsolateSpawnException: ${this.message}`;
     }
   }
   IsolateSpawnException[dart.implements] = () => [core.Exception];
-  dart.setSignature(IsolateSpawnException, {
-    methods: () => ({toString: dart.functionType(core.String, [])})
-  });
+  dart.setSignature(IsolateSpawnException, {});
   let _pause = Symbol('_pause');
   class Isolate extends core.Object {
     Isolate(controlPort, opts) {
       let pauseCapability = opts && 'pauseCapability' in opts ? opts.pauseCapability : null;
       let terminateCapability = opts && 'terminateCapability' in opts ? opts.terminateCapability : null;
       this.controlPort = controlPort;
       this.pauseCapability = pauseCapability;
       this.terminateCapability = terminateCapability;
     }
     static get current() {
@@ skipping 171 matching lines @@
     _IsolateUnhandledException(message, source, stackTrace) {
       this.message = message;
       this.source = source;
       this.stackTrace = stackTrace;
     }
     toString() {
       return 'IsolateUnhandledException: exception while handling message: ' + `${this.message} \n  ` + `${dart.toString(this.source).replaceAll("\n", "\n  ")}\n` + 'original stack trace:\n  ' + `${dart.toString(this.stackTrace).replaceAll("\n", "\n  ")}`;
     }
   }
   _IsolateUnhandledException[dart.implements] = () => [core.Exception];
-  dart.setSignature(_IsolateUnhandledException, {
-    methods: () => ({toString: dart.functionType(core.String, [])})
-  });
+  dart.setSignature(_IsolateUnhandledException, {});
   let _description = Symbol('_description');
   class RemoteError extends core.Object {
     RemoteError(description, stackDescription) {
       this[_description] = description;
       this.stackTrace = new _RemoteStackTrace(stackDescription);
     }
     toString() {
       return this[_description];
     }
   }
   RemoteError[dart.implements] = () => [core.Error];
-  dart.setSignature(RemoteError, {
-    methods: () => ({toString: dart.functionType(core.String, [])})
-  });
+  dart.setSignature(RemoteError, {});
   let _trace = Symbol('_trace');
   class _RemoteStackTrace extends core.Object {
     _RemoteStackTrace(trace) {
       this[_trace] = trace;
     }
     toString() {
       return this[_trace];
     }
   }
   _RemoteStackTrace[dart.implements] = () => [core.StackTrace];
-  dart.setSignature(_RemoteStackTrace, {
-    methods: () => ({toString: dart.functionType(core.String, [])})
-  });
+  dart.setSignature(_RemoteStackTrace, {});
   // Exports:
   exports.Capability = Capability;
   exports.IsolateSpawnException = IsolateSpawnException;
   exports.Isolate = Isolate;
   exports.SendPort = SendPort;
   exports.ReceivePort = ReceivePort;
   exports.RawReceivePort = RawReceivePort;
   exports.RemoteError = RemoteError;
 })(isolate, core, _isolate_helper, async);