Clean up code organization in flutter_tools

1) Moved basic utility code into base/ directory to make it clear which code
   doesn't depend on Flutter-specific knowldge.
2) Move the CommandRunner subclasses into a runner/ directory because these
   aren't commands themselves.

packages/flutter_tools/lib/src/runner/version.dart

diff --git a/packages/flutter_tools/lib/src/runner/version.dart b/packages/flutter_tools/lib/src/runner/version.dart
new file mode 100644
index 0000000..134108f
--- /dev/null
+++ b/packages/flutter_tools/lib/src/runner/version.dart
@@ -0,0 +1,24 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import '../base/process.dart';
+
+String getVersion(String flutterRoot) {
+  String upstream = runSync([
+    'git', 'rev-parse', '--abbrev-ref', '--symbolic', '@{u}'
+  ], workingDirectory: flutterRoot).trim();
+  String repository = '<unknown>';
+  int slash = upstream.indexOf('/');
+  if (slash != -1) {
+    String remote = upstream.substring(0, slash);
+    repository = runSync([
+      'git', 'ls-remote', '--get-url', remote
+    ], workingDirectory: flutterRoot).trim();
+    upstream = upstream.substring(slash + 1);
+  }
+  String revision = runSync([
+    'git', 'log', '-n', '1', '--pretty=format:%H (%ar)'
+  ], workingDirectory: flutterRoot).trim();
+  return 'Flutter\nRepository: $repository\nBranch: $upstream\nRevision: $revision';
+}