Implement device_orientation::Provider.

chrome/browser/device_orientation/orientation.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_DEVICE_ORIENTATION_ORIENTATION_H_
 #define CHROME_BROWSER_DEVICE_ORIENTATION_ORIENTATION_H_
 
 namespace device_orientation {
 class Orientation {
  public:
@@ skipping 16 matching lines @@
 
   Orientation()
       : alpha_(0),
         beta_(0),
         gamma_(0),
         can_provide_alpha_(false),
         can_provide_beta_(false),
         can_provide_gamma_(false) {
   }
 
+  static Orientation Empty() { return Orientation(); }
+
+  bool IsEmpty() {
+    return !can_provide_alpha_ && !can_provide_beta_ && !can_provide_gamma_;
+  }
+
   double alpha_;
   double beta_;
   double gamma_;
   bool can_provide_alpha_;
   bool can_provide_beta_;
   bool can_provide_gamma_;
 };
 
 }  // namespace device_orientation
 
 #endif  // CHROME_BROWSER_DEVICE_ORIENTATION_ORIENTATION_H_