[Sensors] Add README.md files

third_party/WebKit/Source/modules/sensor/README.md

Index: third_party/WebKit/Source/modules/sensor/README.md
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+# Generic Sensor
+
+`third_party/WebKit/Source/modules/sensor` implements the following
+concrete sensor intrefaces based on the [Generic Sensor API] (https://w3c.github.io/sensors):
+
+1. [Ambient Light Sensor] (https://w3c.github.io/ambient-light)
+1. [Accelerometer] (https://w3c.github.io/accelerometer)
+1. [Gyroscope] (https://w3c.github.io/gyroscope)
+1. [Magnetometer] (https://w3c.github.io/magnetometer)
+1. [Absolute Orientation Sensor] (https://w3c.github.io/orientation-sensor)
+
+The platform-specific parts of the implementation are located in `device/generic_sensor`.
+
+
+## Testing
+
+Sensors layout tests are located in `LayoutTests/sensor`.

[Reilly Grant (use Gerrit), 2017/04/13 14:40:41]

Link to LayoutTests/external/wpt/generic-sensor as well? Oh, I see we don't
import those currently. We should.

+
+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) for more details.