Refactors DeviceOrientation to make it more extensible

content/browser/device_orientation/device_data.h

+// Copyright (c) 2012 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 CONTENT_BROWSER_DEVICE_ORIENTATION_DEVICE_DATA_H_
+#define CONTENT_BROWSER_DEVICE_ORIENTATION_DEVICE_DATA_H_
+
+#include <cmath>
+
+namespace device_orientation {
+class DeviceData {
+ public:
+  enum DeviceDataType {
+    kDeviceOrientationData,
+    kNumberOfDeviceDataTypes
+  };
+  virtual ~DeviceData() {}
+
+  virtual DeviceData* Clone() const = 0;
+  virtual bool IsEmpty() const = 0;
+  virtual bool SignificantlyDifferentFrom(const DeviceData& other) = 0;
+  DeviceDataType device_data_type() const { return device_data_type_; }
+
+  static bool IsElementSignificantlyDifferent(bool can_provide_element1,
+      bool can_provide_element2, double element1, double element2) {
+    const double kThreshold = 0.1;
+
+    if (can_provide_element1 != can_provide_element2)

[Steve Block, 2013/05/27 01:36:03]

I'm not sure it makes sense for this to be in the base class. I think this kind
of logic depends on the data type (or even on the provider). For example, for
orientation, if two pieces of data are identical except the newer data can't
provide a certain property, the provider probably shouldn't update its listeners
with this.

+      return true;
+    if (can_provide_element1 && std::fabs(element1 - element2) >= kThreshold)
+      return true;
+    return false;
+  }
+
+ protected:
+   DeviceDataType device_data_type_;
+};
+
+}  // namespace device_orientation
+
+#endif  // CONTENT_BROWSER_DEVICE_ORIENTATION_DEVICE_DATA_H_