add sendRequest to VMIsolateRef

lib/src/isolate.dart

Index: lib/src/isolate.dart
diff --git a/lib/src/isolate.dart b/lib/src/isolate.dart
index d9363daa37947af26664dde7e475026e8286fba8..d2f876c9966fc1cdc01ca643edd598b788d23250 100644
--- a/lib/src/isolate.dart
+++ b/lib/src/isolate.dart
@@ -264,6 +264,22 @@ class VMIsolateRef {
     }
   }
 
+  /// Makes a raw RPC to a VM service extension registered in the isolate
+  /// corresponding to the ID [number].
+  ///
+  /// [method] must correspond to a VM service extension installed on the VM
+  /// isolate and it must begin with prefix "ext.".
+  ///
+  /// [params] are passed to the extension handler and must be serializable to
+  /// a JSON string.
+  Future<Map> invokeExtension(String method, [Map<String, Object> params]) {
+    if (!method.startsWith('ext.')) {
+      throw new ArgumentError.value(method, 'method',
+          'must begin with "ext." prefix');
+    }
+    return _scope.sendRequest(method, params);
+  }
+
   bool operator ==(other) => other is VMIsolateRef &&
       other._scope.isolateId == _scope.isolateId;
 
@@ -365,4 +381,4 @@ class VMStep {
   const VMStep._(this._value);
 
   String toString() => _value;
-}
+}