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diff --git a/widget/gonk/ProcessOrientation.h b/widget/gonk/ProcessOrientation.h
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+/*
+ * Copyright (c) 2013, Linux Foundation. All rights reserved
+ *
+ * Copyright (C) 2008 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ProcessOrientation_h
+#define ProcessOrientation_h
+
+#include "mozilla/Hal.h"
+
+namespace mozilla {
+
+// History of observed tilt angles.
+#define TILT_HISTORY_SIZE 40
+
+class ProcessOrientation {
+public:
+  ProcessOrientation() {};
+  ~ProcessOrientation() {};
+
+  int OnSensorChanged(const mozilla::hal::SensorData& event, int deviceCurrentRotation);
+  int Reset();
+
+private:
+  int GetProposedRotation();
+
+  // Returns true if the tilt angle is acceptable for a given predicted
+  // rotation.
+  bool IsTiltAngleAcceptable(int rotation, int tiltAngle);
+
+  // Returns true if the orientation angle is acceptable for a given predicted
+  // rotation. This function takes into account the gap between adjacent
+  // orientations for hysteresis.
+  bool IsOrientationAngleAcceptable(int rotation, int orientationAngle,
+                                    int currentRotation);
+
+  // Returns true if the predicted rotation is ready to be advertised as a
+  // proposed rotation.
+  bool IsPredictedRotationAcceptable(int64_t now);
+
+  void ClearPredictedRotation();
+  void UpdatePredictedRotation(int64_t now, int rotation);
+  bool IsAccelerating(float magnitude);
+  void ClearTiltHistory();
+  void AddTiltHistoryEntry(int64_t now, float tilt);
+  bool IsFlat(int64_t now);
+  bool IsSwinging(int64_t now, float tilt);
+  int NextTiltHistoryIndex(int index);
+  float RemainingMS(int64_t now, int64_t until);
+
+  // The tilt angle range in degrees for each orientation. Beyond these tilt
+  // angles, we don't even consider transitioning into the specified orientation.
+  // We place more stringent requirements on unnatural orientations than natural
+  // ones to make it less likely to accidentally transition into those states.
+  // The first value of each pair is negative so it applies a limit when the
+  // device is facing down (overhead reading in bed). The second value of each
+  // pair is positive so it applies a limit when the device is facing up
+  // (resting on a table). The ideal tilt angle is 0 (when the device is vertical)
+  // so the limits establish how close to vertical the device must be in order
+  // to change orientation.
+  static const int tiltTolerance[][4];
+
+  // Timestamp and value of the last accelerometer sample.
+  int64_t mLastFilteredTimestampNanos;
+  float mLastFilteredX, mLastFilteredY, mLastFilteredZ;
+
+  // The last proposed rotation, -1 if unknown.
+  int mProposedRotation;
+
+  // Value of the current predicted rotation, -1 if unknown.
+  int mPredictedRotation;
+
+  // Timestamp of when the predicted rotation most recently changed.
+  int64_t mPredictedRotationTimestampNanos;
+
+  // Timestamp when the device last appeared to be flat for sure (the flat delay
+  // elapsed).
+  int64_t mFlatTimestampNanos;
+
+  // Timestamp when the device last appeared to be swinging.
+  int64_t mSwingTimestampNanos;
+
+  // Timestamp when the device last appeared to be undergoing external
+  // acceleration.
+  int64_t mAccelerationTimestampNanos;
+
+  struct {
+    struct {
+      float tiltAngle;
+      int64_t timestampNanos;
+    } history[TILT_HISTORY_SIZE];
+    int index;
+  } mTiltHistory;
+};
+
+} // namespace mozilla
+
+#endif