[sensors] Android platform adaptation for Generic Sensor API

device/generic_sensor/android/java/src/org/chromium/device/sensors/PlatformSensorProvider.java

+// Copyright 2016 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.
+
+package org.chromium.device.sensors;
+
+import android.content.Context;
+import android.hardware.Sensor;
+import android.hardware.SensorManager;
+import android.os.Handler;
+import android.os.HandlerThread;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+import org.chromium.mojom.device.mojom.SensorType;
+
+/**
+ * Lifetime is controlled by device::PlatformSensorProviderAndroid.
+ */
+@JNINamespace("device")
+final class PlatformSensorProvider {
+    private final SensorManager mSensorManager;
+    private final HandlerThread mSensorsThread;
+    private final Handler mHandler;
+
+    private PlatformSensorProvider(Context context) {
+        mSensorManager = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
+
+        if (mSensorManager != null) {
+            mSensorsThread = new HandlerThread("SensorsHandlerThread");

[Ted C, 2016/09/01 00:12:36]

what thread are sensors handled on for other platforms?

Also, should we be terminating this thread at some point?  Should we only run
this if any sensors are active?

[shalamov, 2016/09/06 12:36:43]

Added code that starts / stops thread when there are active sensors.

+            mSensorsThread.start();
+            mHandler = new Handler(mSensorsThread.getLooper());
+        } else {
+            mSensorsThread = null;
+            mHandler = null;
+        }
+    }
+
+    @CalledByNative
+    private static PlatformSensorProvider create(Context context) {
+        return new PlatformSensorProvider(context);
+    }
+
+    @CalledByNative
+    private PlatformSensor createSensor(int type) {
+        if (mSensorManager == null || mHandler == null) return null;
+
+        try {
+            switch (type) {
+                case SensorType.AMBIENT_LIGHT:
+                    return new GenericPlatformSensor(
+                            Sensor.TYPE_LIGHT, 1, mSensorManager, mHandler);
+                case SensorType.ACCELEROMETER:
+                    return new GenericPlatformSensor(
+                            Sensor.TYPE_ACCELEROMETER, 3, mSensorManager, mHandler);
+                case SensorType.LINEAR_ACCELERATION:
+                    return new GenericPlatformSensor(
+                            Sensor.TYPE_LINEAR_ACCELERATION, 3, mSensorManager, mHandler);
+                case SensorType.GYROSCOPE:
+                    return new GenericPlatformSensor(
+                            Sensor.TYPE_GYROSCOPE, 3, mSensorManager, mHandler);
+                case SensorType.MAGNETOMETER:
+                    return new GenericPlatformSensor(
+                            Sensor.TYPE_MAGNETIC_FIELD, 3, mSensorManager, mHandler);
+            }
+        } catch (PlatformSensorException e) {
+            return null;
+        }
+
+        return null;
+    }
+}