Add README for Chromium sensor backend modernization on Windows.

This document introduces the proposed design changes for modernizing
the Chromium sensor backend on Windows allowing it to use the new
Windows.Devices.Sensor WinRT APIs instead of the deprecated ISensor Win32 API.

This README will not cover the context or justification for the
modernization work as it is already captured by this document:
https://docs.google.com/document/d/1Vr5xXOu4v-H6ydeCJed1bU_WR9kBYm3ANV-GB-JPZuw/edit?usp=sharing

The new README file also reads more like a future looking document
(contains "will do this..." and "proposed") since it not implemented yet.

Change-Id: Ibcfeb9020bd930d50ab9898ce0ee145c9e645e1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1664111
Commit-Queue: Wenjie Shi <wensh@microsoft.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672220}

services/device/generic_sensor/README.md

@@ -64,15 +64,15 @@ platform.
 
 | SensorType                        | Android                   | Linux                                 | macOS                                 | Windows                                   |
 | --------------------------------- | ------------------------- | ------------------------------------- | ------------------------------------- | ----------------------------------------- |
-| AMBIENT_LIGHT                     | TYPE_LIGHT                | in_illuminance                        | AppleLMUController                    | SENSOR_TYPE_AMBIENT_LIGHT                 |
+| AMBIENT_LIGHT                     | TYPE_LIGHT                | in_illuminance                        | AppleLMUController                    | Yes                                       |
 | PROXIMITY                         |                           |                                       |                                       |                                           |
-| ACCELEROMETER                     | TYPE_ACCELEROMETER        | in_accel                              | SMCMotionSensor                       | SENSOR_TYPE_ACCELEROMETER_3D              |
+| ACCELEROMETER                     | TYPE_ACCELEROMETER        | in_accel                              | SMCMotionSensor                       | Yes                                       |
 | LINEAR_ACCELEROMETER              | See below                 | ACCELEROMETER (*)                     |                                       | ACCELEROMETER (*)                         |
-| GYROSCOPE                         | TYPE_GYROSCOPE            | in_anglvel                            |                                       | SENSOR_TYPE_GYROMETER_3D                  |
-| MAGNETOMETER                      | TYPE_MAGNETIC_FIELD       | in_magn                               |                                       | SENSOR_TYPE_COMPASS_3D                    |
+| GYROSCOPE                         | TYPE_GYROSCOPE            | in_anglvel                            |                                       | Yes                                       |
+| MAGNETOMETER                      | TYPE_MAGNETIC_FIELD       | in_magn                               |                                       | Yes                                       |
 | PRESSURE                          |                           |                                       |                                       |                                           |
-| ABSOLUTE_ORIENTATION_EULER_ANGLES | See below                 | ACCELEROMETER and MAGNETOMETER (*)    |                                       | SENSOR_TYPE_INCLINOMETER_3D               |
-| ABSOLUTE_ORIENTATION_QUATERNION   | See below                 | ABSOLUTE_ORIENTATION_EULER_ANGLES (*) |                                       | SENSOR_TYPE_AGGREGATED_DEVICE_ORIENTATION |
+| ABSOLUTE_ORIENTATION_EULER_ANGLES | See below                 | ACCELEROMETER and MAGNETOMETER (*)    |                                       | Yes                                       |
+| ABSOLUTE_ORIENTATION_QUATERNION   | See below                 | ABSOLUTE_ORIENTATION_EULER_ANGLES (*) |                                       | Yes                                       |
 | RELATIVE_ORIENTATION_EULER_ANGLES | See below                 | ACCELEROMETER and GYROSCOPE (*)       | ACCELEROMETER (*)                     |                                           |
 |                                   |                           | or ACCELEROMETER (*)                  |                                       |                                           |
 | RELATIVE_ORIENTATION_QUATERNION   | TYPE_GAME_ROTATION_VECTOR | RELATIVE_ORIENTATION_EULER_ANGLES (*) | RELATIVE_ORIENTATION_EULER_ANGLES (*) |                                           |
@@ -132,13 +132,7 @@ value that can be read from the RELATIVE_ORIENTATION_EULER_ANGLES.
 
 ### Windows
 
-Sensors are implemented by passing through values provided by the
-[Sensor API](https://msdn.microsoft.com/en-us/library/windows/desktop/dd318953(v=vs.85).aspx).
-The values in the "Windows" column of the table above correspond to the names of
-the sensor type GUIDs used to provide data for a SensorType. The
-LINEAR_ACCELEROMETER sensor type is provided by implementing a low-pass-filter
-over the values returned by the ACCELEROMETER in order to remove the
-contribution of the gravitational force.
+Please refer to this [document](windows/README.md).
 
 ## Testing
 
@@ -150,7 +144,6 @@ The sensors unit tests file for Android is
 
 Sensors browser tests are located in `content/test/data/generic_sensor`.
 
-
 ## Design Documents
 
 Please refer to the [design documentation](https://docs.google.com/document/d/1Ml65ZdW5AgIsZTszk4mD_ohr40pcrdVFOIf0ZtWxDv0)