Implement device_orientation::Provider.

chrome/browser/device_orientation/orientation.h

Index: chrome/browser/device_orientation/orientation.h
diff --git a/chrome/browser/device_orientation/orientation.h b/chrome/browser/device_orientation/orientation.h
index d43a989b1a985a3fd675e9218292de335dfe17c9..2193170991e745d419a8a83b854e224e4ff4408c 100644
--- a/chrome/browser/device_orientation/orientation.h
+++ b/chrome/browser/device_orientation/orientation.h
@@ -34,6 +34,12 @@ class Orientation {
         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_;