Initial sketch of install command and what devices look like.

packages/flutter_tools/lib/src/device.dart

diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
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+// 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.
+
+library sky_tools.device;
+
+abstract class _Device {
+  final String id;
+  static Map<String, _Device> _deviceCache = {};
+
+  factory _Device(String className, [String id = null]) {
+    if (id == null) {
+      if (className == AndroidDevice.className) {
+        id = AndroidDevice.defaultDeviceID;
+      } else {
+        throw 'Attempted to create a Device of unknown type $className';
+      }
+    }
+
+    return _deviceCache.putIfAbsent(id, () {
+      if (className == AndroidDevice.className) {
+        final device = new AndroidDevice._(id);
+        _deviceCache[id] = device;
+        return device;
+      } else {
+        throw 'Attempted to create a Device of unknown type $className';
+      }
+    });
+  }
+
+  _Device._(this.id);
+
+  /// Install an app package on the current device
+  bool installApp(String path);
+
+  /// Check if the current device needs an installation
+  bool needsInstall();
+
+  /// Check if the device is currently connected
+  bool isConnected();
+}
+
+class AndroidDevice extends _Device {
+  static const String className = 'AndroidDevice';
+  static final String defaultDeviceID = 'default';
+
+  factory AndroidDevice([String id = null]) {
+    return new _Device(className, id);
+  }
+
+  AndroidDevice._(id) : super._(id);
+
+  @override
+  bool installApp(String path) {
+    return false;
+  }
+
+  @override
+  bool needsInstall() {
+    return true;
+  }
+
+  @override
+  bool isConnected() {
+    return true;
+  }
+}