Implement the content/renderer and content/browser part of the Device Motion API.

content/common/device_motion_messages.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.
 
 // IPC messages for device motion.
 // Multiply-included message file, hence no include guard.
 
 #include "ipc/ipc_message_macros.h"
+#include "ipc/ipc_param_traits.h"
+#include "ipc/ipc_platform_file.h"
+#include "base/shared_memory.h"
 
 #define IPC_MESSAGE_START DeviceMotionMsgStart
 
+// Messages sent from the renderer to the browser.
+
+// Asks the browser process to start polling, and return a shared memory
+// handles that will hold the data from the hardware. See
+// device_motion_hardware_buffer.h for a description of how synchronization is
+// handled. The number of Starts should match the number of Stops.
+IPC_SYNC_MESSAGE_CONTROL0_1(DeviceMotionHostMsg_StartPolling,

[jamesr, 2013/05/16 19:58:21]

Why synchronous?

[timvolodine, 2013/05/20 18:18:48]

we need a valid handle to the shared memory from the browser before we start
polling.

The actual call is not completely synchronous anyway, in the sense that we don't
wait for sensors to start firing, just a shared memory buffer handle needs to be
returned.

+                            base::SharedMemoryHandle /* handle */)
+
+IPC_SYNC_MESSAGE_CONTROL0_0(DeviceMotionHostMsg_StopPolling)

[jamesr, 2013/05/16 19:58:21]

Ditto - why synchronous?

[timvolodine, 2013/05/20 18:18:48]

this can be async. Done.

+
+// TODO(timvolodine): remove the methods below once the Device Motion
+// is implemented.
+
 IPC_STRUCT_BEGIN(DeviceMotionMsg_Updated_Params)
   // These fields have the same meaning as in device_motion::Motion.
   IPC_STRUCT_MEMBER(bool, can_provide_acceleration_x)
   IPC_STRUCT_MEMBER(double, acceleration_x)
   IPC_STRUCT_MEMBER(bool, can_provide_acceleration_y)
   IPC_STRUCT_MEMBER(double, acceleration_y)
   IPC_STRUCT_MEMBER(bool, can_provide_acceleration_z)
   IPC_STRUCT_MEMBER(double, acceleration_z)
   IPC_STRUCT_MEMBER(bool, can_provide_acceleration_including_gravity_x)
   IPC_STRUCT_MEMBER(double, acceleration_including_gravity_x)
@@ skipping 19 matching lines @@
 
 // Messages sent from the renderer to the browser.
 
 // A RenderView requests to start receiving device motion updates.
 IPC_MESSAGE_CONTROL1(DeviceMotionHostMsg_StartUpdating,
                      int /* render_view_id */)
 
 // A RenderView requests to stop receiving device motion updates.
 IPC_MESSAGE_CONTROL1(DeviceMotionHostMsg_StopUpdating,
                      int /* render_view_id */)