Reland of [sensors] Ambient light sensor implementation for ChromeOS and Linux.

device/generic_sensor/platform_sensor_provider_linux.h

Index: device/generic_sensor/platform_sensor_provider_linux.h
diff --git a/device/generic_sensor/platform_sensor_provider_linux.h b/device/generic_sensor/platform_sensor_provider_linux.h
new file mode 100644
index 0000000000000000000000000000000000000000..7470cbeb82edcae0c03c4dde49c497cb2c2f8947
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+++ b/device/generic_sensor/platform_sensor_provider_linux.h
@@ -0,0 +1,75 @@
+// 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_PUBLIC_PLATFORM_SENSOR_PROVIDER_LINUX_H_
+#define DEVICE_GENERIC_SENSOR_PUBLIC_PLATFORM_SENSOR_PROVIDER_LINUX_H_
+
+#include "device/generic_sensor/platform_sensor_provider.h"
+
+namespace base {
+class Thread;
+}
+
+namespace device {
+
+struct SensorDataLinux;
+class SensorReader;
+
+class PlatformSensorProviderLinux : public PlatformSensorProvider {
+ public:
+  PlatformSensorProviderLinux();
+  ~PlatformSensorProviderLinux() override;
+
+  static PlatformSensorProviderLinux* GetInstance();
+
+ protected:
+  void CreateSensorInternal(mojom::SensorType type,
+                            mojo::ScopedSharedBufferMapping mapping,
+                            const CreateSensorCallback& callback) override;
+
+  void AllSensorsRemoved() override;
+
+  void SetFileTaskRunner(
+      scoped_refptr<base::SingleThreadTaskRunner> file_task_runner) override;
+
+ private:
+  void SensorReaderFound(
+      mojom::SensorType type,
+      mojo::ScopedSharedBufferMapping mapping,
+      const PlatformSensorProviderBase::CreateSensorCallback& callback,
+      const SensorDataLinux& data,
+      std::unique_ptr<SensorReader> sensor_reader);
+
+  // Stops a polling thread if there are no sensors left. Must be called on
+  // a different that polling thread that allows io.
+  void StopPollingThread();
+
+  // TODO(maksims): make a separate class Manager that will
+  // create provide sensors with a polling task runner, check sensors existence
+  // and notify provider if a new sensor has appeared and it can be created if a
+  // request comes again for the same sensor.
+  // A use case example: a request for a sensor X comes, manager checks if the
+  // sensor exists on a platform and notifies a provider it is not found.
+  // The provider stores this information into its cache and doesn't try to
+  // create this specific sensor if a request comes. But when, for example,
+  // the sensor X is plugged into a usb port, the manager notices that and
+  // notifies the provider, which updates its cache and starts handling requests
+  // for the sensor X.
+  //
+  // Right now, this thread is used to find sensors files and poll data.
+  std::unique_ptr<base::Thread> polling_thread_;
+
+  // A task runner that is passed to polling sensors to poll data.
+  scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner_;
+
+  // Browser's file thread task runner passed from renderer. Used to
+  // stop a polling thread.
+  scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(PlatformSensorProviderLinux);
+};
+
+}  // namespace device
+
+#endif  // DEVICE_GENERIC_SENSOR_PUBLIC_PLATFORM_SENSOR_PROVIDER_LINUX_H_