Removed fixed dependencies

packages/usage/lib/usage_io.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/// In order to use this library import the `usage_io.dart` file and
-/// instantiate the [AnalyticsIO] class.
-///
-/// You'll need to provide a Google Analytics tracking ID, the application name,
-/// and the application version.
+/**
+ * In order to use this library import the `usage_io.dart` file and
+ * instantiate the [AnalyticsIO] class.
+ *
+ * You'll need to provide a Google Analytics tracking ID, the application name,
+ * and the application version.
+ */
 library usage_io;
 
-export 'src/usage_impl_io.dart' show AnalyticsIO;
+import 'src/usage_impl.dart';
+import 'src/usage_impl_io.dart';
+
 export 'usage.dart';
+
+/**
+ * An interface to a Google Analytics session, suitable for use in command-line
+ * applications.
+ *
+ * [analyticsUrl] is an optional replacement for the default Google Analytics
+ * URL (`https://www.google-analytics.com/collect`).
+ */
+class AnalyticsIO extends AnalyticsImpl {
+  AnalyticsIO(String trackingId, String applicationName, String applicationVersion, {
+    String analyticsUrl
+  }) : super(
+    trackingId,
+    new IOPersistentProperties(applicationName),
+    new IOPostHandler(),
+    applicationName: applicationName,
+    applicationVersion: applicationVersion,
+    analyticsUrl: analyticsUrl
+  );
+}