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

device/generic_sensor/polling_platform_sensor.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/polling_platform_sensor.h"
+
+#include "base/message_loop/message_loop.h"
+
+namespace device {
+
+PollingPlatformSensor::Deleter::Deleter() = default;
+PollingPlatformSensor::Deleter::~Deleter() = default;
+
+void PollingPlatformSensor::Deleter::operator()(
+    base::RepeatingTimer* timer) const {
+  DCHECK(task_runner_);
+  task_runner_->PostTask(FROM_HERE, base::Bind(&Deleter::destroy_timer,
+                                               base::Unretained(this), timer));
+}
+
+PollingPlatformSensor::PollingPlatformSensor(
+    mojom::SensorType type,
+    mojo::ScopedSharedBufferMapping mapping,
+    PlatformSensorProvider* provider,
+    scoped_refptr<base::SingleThreadTaskRunner> ipc_task_runner)
+    : PlatformSensor(type, std::move(mapping), provider),
+      polling_thread_task_runner_(base::MessageLoop::current()->task_runner()),
+      ipc_task_runner_(ipc_task_runner),
+      weak_factory_(this) {}
+
+PollingPlatformSensor::~PollingPlatformSensor() = default;
+
+bool PollingPlatformSensor::StartSensor(
+    const PlatformSensorConfiguration& configuration) {
+  return polling_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PollingPlatformSensor::BeginPoll,
+                            weak_factory_.GetWeakPtr(), configuration));
+}
+
+void PollingPlatformSensor::BeginPoll(
+    const PlatformSensorConfiguration& configuration) {
+  timer_.reset(new base::RepeatingTimer());
+  timer_.get_deleter().set_helper(polling_thread_task_runner_);
+  timer_->Start(FROM_HERE, base::TimeDelta::FromMicroseconds(
+                               base::Time::kMicrosecondsPerSecond /
+                               configuration.frequency()),
+                this, &PollingPlatformSensor::UpdateReading);
+}
+
+void PollingPlatformSensor::StopSensor() {
+  polling_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PollingPlatformSensor::StopPoll, this));
+}
+
+void PollingPlatformSensor::StopPoll() {
+  timer_->Stop();
+}
+
+}  // namespace device