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

device/generic_sensor/platform_sensor_provider_base.cc

 // 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.
 
 #include "device/generic_sensor/platform_sensor_provider_base.h"
 
 #include <utility>
 
 #include "base/stl_util.h"
 #include "device/generic_sensor/public/interfaces/sensor_provider.mojom.h"
@@ skipping 61 matching lines @@
   shared_buffer_handle_ =
       mojo::SharedBufferHandle::Create(kSharedBufferSizeInBytes);
   return shared_buffer_handle_.is_valid();
 }
 
 void PlatformSensorProviderBase::RemoveSensor(mojom::SensorType type) {
   DCHECK(CalledOnValidThread());
   DCHECK(ContainsKey(sensor_map_, type));
   sensor_map_.erase(type);
 
-  if (sensor_map_.empty())
+  if (sensor_map_.empty()) {
+    AllSensorsRemoved();
     shared_buffer_handle_.reset();
+  }
 }
 
 mojo::ScopedSharedBufferHandle
 PlatformSensorProviderBase::CloneSharedBufferHandle() {
   DCHECK(CalledOnValidThread());
   CreateSharedBufferIfNeeded();
   return shared_buffer_handle_->Clone(
       mojo::SharedBufferHandle::AccessMode::READ_ONLY);
 }
 
+bool PlatformSensorProviderBase::HasSensors() const {
+  DCHECK(CalledOnValidThread());
+  return !sensor_map_.empty();
+}
+
 void PlatformSensorProviderBase::NotifySensorCreated(
     mojom::SensorType type,
     scoped_refptr<PlatformSensor> sensor) {
   DCHECK(CalledOnValidThread());
   DCHECK(!ContainsKey(sensor_map_, type));
   DCHECK(ContainsKey(requests_map_, type));
 
   if (sensor)
     sensor_map_[type] = sensor.get();
 
   // Inform subscribers about the sensor.
   // |sensor| can be nullptr here.
   auto it = requests_map_.find(type);
   for (auto& callback : it->second)
     callback.Run(sensor);
 
   requests_map_.erase(type);
 }
 
 }  // namespace device