Fix. typos in leak_tracker (#234)

Thank you!!!

pkgs/leak_tracker/lib/src/devtools_integration/_registration.dart

@@ -12,7 +12,7 @@ import 'delivery.dart';
 import 'messages.dart';
 import 'primitives.dart';
 
-bool _extentsionRegistered = false;
+bool _extensionRegistered = false;
 
 /// Registers service extension to signal that leak tracking is
 /// already enabled and other leak tracking systems
@@ -76,13 +76,13 @@ bool _registerServiceExtension(
   Future<ServiceExtensionResponse> Function(String, Map<String, String>)
       handler,
 ) {
-  if (_extentsionRegistered) return false;
+  if (_extensionRegistered) return false;
   try {
     registerExtension(
       memoryLeakTrackingExtensionName,
       handler,
     );
-    _extentsionRegistered = true;
+    _extensionRegistered = true;
 
     return true;
     // ignore: avoid_catching_errors

pkgs/leak_tracker/lib/src/leak_tracking/primitives/model.dart

@@ -148,7 +148,7 @@ class IgnoredLeaks {
   /// start of leak tracking contains a frame, located after the test body
   /// frame, that points to the folder `test` or the package `flutter_test`,
   /// except:
-  /// * methods intended to be called from test body like `runAsunc` or `pump`
+  /// * methods intended to be called from test body like `runAsync` or `pump`
   /// * frames that match [testHelperExceptions]
   final bool createdByTestHelpers;
 

pkgs/leak_tracker/lib/src/shared/_primitives.dart

@@ -5,7 +5,7 @@
 /// Result of [identityHashCode].
 typedef IdentityHashCode = int;
 
-/// Finilizer builder to mock standard [identityHashCode].
+/// Finalizer builder to mock standard [identityHashCode].
 typedef IdentityHashCoder = IdentityHashCode Function(Object object);
 
 int standardIdentityHashCoder(Object object) => identityHashCode(object);