[sensors] PlatformSensorProvider implementations are notified when there are no sensor instances

device/generic_sensor/platform_sensor_provider_base.h

Index: device/generic_sensor/platform_sensor_provider_base.h
diff --git a/device/generic_sensor/platform_sensor_provider_base.h b/device/generic_sensor/platform_sensor_provider_base.h
index 6244170e86a61c0218f86652393192fdb37c6c8f..91ba9e004a118a4d5c308da54ebde493ea69a01b 100644
--- a/device/generic_sensor/platform_sensor_provider_base.h
+++ b/device/generic_sensor/platform_sensor_provider_base.h
@@ -38,6 +38,10 @@ class PlatformSensorProviderBase : public base::NonThreadSafe {
                                     mojo::ScopedSharedBufferMapping mapping,
                                     const CreateSensorCallback& callback) = 0;
 
+  // Implementations might override this method to free resources when there
+  // are no sensors left.
+  virtual void AllSensorsRemoved() {}

[shalamov, 2016/10/20 06:37:26]

Can you also add bool HasSensors() const;

+
  private:
   friend class PlatformSensor;  // To call RemoveSensor();