[sensors](CrOS/Linux) Implement Sensor device manager for sensors

device/generic_sensor/platform_sensor_manager_linux.h

Index: device/generic_sensor/platform_sensor_manager_linux.h
diff --git a/device/generic_sensor/platform_sensor_manager_linux.h b/device/generic_sensor/platform_sensor_manager_linux.h
new file mode 100644
index 0000000000000000000000000000000000000000..cbe5dc786b577e2ae1773f355fb209a1c1a666f1
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+++ b/device/generic_sensor/platform_sensor_manager_linux.h
@@ -0,0 +1,83 @@
+// 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_MANAGER_LINUX_H_
+#define DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_MANAGER_LINUX_H_
+
+#include "base/scoped_observer.h"
+
+#include "device/base/device_monitor_linux.h"
+#include "device/generic_sensor/public/interfaces/sensor.mojom.h"
+
+namespace device {
+
+struct SensorInfoLinux;
+
+// This SensorDeviceManager uses LinuxDeviceMonitor to enumerate devices
+// and listen to "add/removed" events to notify |provider_| about
+// added or removed iio devices. It has own cache to speed up an identification
+// process of removed devices.
+class DEVICE_GENERIC_SENSOR_EXPORT SensorDeviceManager
+    : public DeviceMonitorLinux::Observer {
+ public:
+  class Delegate {
+   public:
+    // Called when SensorDeviceManager has enumerated through all possible
+    // iio udev devices.
+    virtual void OnEnumerationReady() = 0;
+
+    // Called after SensorDeviceManager has identified a udev device, which
+    // belongs to "iio" subsystem.
+    virtual void OnDeviceAdded(mojom::SensorType type,
+                               std::unique_ptr<SensorInfoLinux> sensor) = 0;
+
+    // Called after "removed" event is received from LinuxDeviceMonitor and
+    // sensor is identified as known.
+    virtual void OnDeviceRemoved(mojom::SensorType type,
+                                 const std::string& device_node) = 0;
+
+   protected:
+    virtual ~Delegate() {}
+  };
+
+  SensorDeviceManager();
+  ~SensorDeviceManager() override;
+
+  // Starts this service.
+  virtual void Start(Delegate* delegate);
+
+ protected:
+  using SensorDeviceMap = std::unordered_map<std::string, mojom::SensorType>;
+
+  // Wrappers around udev system methods that can be implemented differently
+  // by tests.
+  virtual std::string GetUdevDeviceGetSubsystem(udev_device* dev);
+  virtual std::string GetUdevDeviceGetSyspath(udev_device* dev);
+  virtual std::string GetUdevDeviceGetSysattrValue(
+      udev_device* dev,
+      const std::string& attribute);
+  virtual std::string GetUdevDeviceGetDevnode(udev_device* dev);
+
+  // DeviceMonitorLinux::Observer:
+  void OnDeviceAdded(udev_device* udev_device) override;
+  void OnDeviceRemoved(udev_device* device) override;
+
+  // Represents a map of sensors that are already known to this manager after
+  // initial enumeration.
+  SensorDeviceMap sensors_by_node_;
+
+  base::ThreadChecker thread_checker_;
+  ScopedObserver<DeviceMonitorLinux, DeviceMonitorLinux::Observer> observer_;
+
+  Delegate* delegate_;
+
+  // A task runner, which |delegate_| lives on.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(SensorDeviceManager);
+};
+
+}  // namespace device
+
+#endif  // DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_MANAGER_LINUX_H_