[sensors] Introduce Generic Sensor API interfaces

device/generic_sensor/platform_sensor_provider_base.h

+// 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.
+
+#ifndef DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_PROVIDER_BASE_H_
+#define DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_PROVIDER_BASE_H_
+
+#include "base/macros.h"
+
+#include "base/threading/non_thread_safe.h"
+#include "device/generic_sensor/platform_sensor.h"
+
+namespace device {
+
+// Base class that defines factory methods for PlatformSensor creation.
+// Its implementations must be accessed via GetInstance() method.
+class PlatformSensorProviderBase : public base::NonThreadSafe {
+ public:
+  // Returns the PlatformSensorProviderBase singleton.
+  // Note: returns 'nullptr' if there is no available implementation for
+  // the current platform.
+  static PlatformSensorProviderBase* GetInstance();
+
+  // Creates new instance of PlatformSensor.
+  scoped_refptr<PlatformSensor> CreateSensor(mojom::SensorType type,
+                                             uint64_t size,
+                                             uint64_t offset);
+
+  // Gets previously created instance of PlatformSensor by sensor type |type|.
+  scoped_refptr<PlatformSensor> GetSensor(mojom::SensorType type);
+
+  // Shared buffer getters.
+  mojo::ScopedSharedBufferHandle CloneSharedBufferHandle();
+
+ protected:
+  PlatformSensorProviderBase();
+  virtual ~PlatformSensorProviderBase();
+
+  // Method that must be implemented by platform specific classes.
+  virtual scoped_refptr<PlatformSensor> CreateSensorInternal(
+      mojom::SensorType type,
+      mojo::ScopedSharedBufferMapping mapping,
+      uint64_t buffer_size) = 0;
+
+ private:
+  friend class PlatformSensor;  // To call RemoveSensor();
+
+  bool CreateSharedBufferIfNeeded();
+  void RemoveSensor(mojom::SensorType type);
+
+ private:
+  std::map<mojom::SensorType, PlatformSensor*> sensor_map_;
+  mojo::ScopedSharedBufferHandle shared_buffer_handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(PlatformSensorProviderBase);
+};
+
+}  // namespace device
+
+#endif  // DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_PROVIDER_BASE_H_