Implement the Blink part of the Device Motion API.

Source/Platform/chromium/public/WebDeviceMotionData.h

+/*
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+ * modification, are permitted provided that the following conditions are
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+ */
+
+#ifndef WebDeviceMotionData_h
+#define WebDeviceMotionData_h
+
+#if WEBKIT_IMPLEMENTATION
+namespace WTF { template <typename T> class PassRefPtr; }
+namespace WebCore { class DeviceMotionData; }
+#endif
+
+namespace WebKit {
+
+#pragma pack(push, 1)

[Peter Beverloo, 2013/04/29 17:38:03]

Is this class really that important from a memory pressure point of view?  How
many copies do you expect there to be?  You save 8 bytes (7 + padding) by doing
this.  Nonetheless, it's a minor win..

[timvolodine, 2013/04/30 12:40:18]

It's probably not very important, but this results in smaller mem-copy @50Hz.
This is also how Gamepad API is done.

+
+class WebDeviceMotionData {
+public:
+    WebDeviceMotionData();
+    ~WebDeviceMotionData() { }
+
+    void setAccelerationX(double);
+    void setAccelerationY(double);
+    void setAccelerationZ(double);
+
+    void setAccelerationIncludingGravityX(double);
+    void setAccelerationIncludingGravityY(double);
+    void setAccelerationIncludingGravityZ(double);
+
+    void setRotationRateAlpha(double);
+    void setRotationRateBeta(double);
+    void setRotationRateGamma(double);
+
+    void setInterval(double);
+
+#if WEBKIT_IMPLEMENTATION
+    operator WTF::PassRefPtr<WebCore::DeviceMotionData>() const;
+#endif
+
+private:
+    double m_accelerationX;
+    double m_accelerationY;
+    double m_accelerationZ;
+
+    double m_accelerationIncludingGravityX;
+    double m_accelerationIncludingGravityY;
+    double m_accelerationIncludingGravityZ;
+
+    double m_rotationRateAlpha;
+    double m_rotationRateBeta;
+    double m_rotationRateGamma;
+
+    double m_interval;
+
+    char m_hasAccelerationX : 1;
+    char m_hasAccelerationY : 1;
+    char m_hasAccelerationZ : 1;
+
+    char m_hasAccelerationIncludingGravityX : 1;
+    char m_hasAccelerationIncludingGravityY : 1;
+    char m_hasAccelerationIncludingGravityZ : 1;
+
+    char m_hasRotationRateAlpha : 1;
+    char m_hasRotationRateBeta : 1;
+    char m_hasRotationRateGamma : 1;
+};
+
+#if WEBKIT_IMPLEMENTATION
+COMPILE_ASSERT(sizeof(WebDeviceMotionData) == (10*8 + 2), WebDeviceMotionData_has_wrong_size);
+#endif
+
+#pragma pack(pop)
+
+} // namespace WebKit
+
+#endif // WebDeviceMotionData_h