[sensors]: Introduce the Generic Sensor API.

third_party/WebKit/Source/modules/sensor/Sensor.cpp

+// 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 "modules/sensor/Sensor.h"
+
+#include "core/dom/Document.h"
+#include "core/dom/ExceptionCode.h"
+#include "core/dom/ExecutionContextTask.h"
+#include "core/events/Event.h"
+
+#include "modules/sensor/SensorReading.h"
+
+namespace blink {
+
+Sensor::~Sensor()
+{
+}
+
+Sensor::Sensor(ExecutionContext* executionContext, const SensorOptions& sensorOptions)
+    : ActiveScriptWrappable(this)
+    , ActiveDOMObject(executionContext)
+    , PlatformEventController(toDocument(executionContext)->page())
+    , m_sensorState(SensorState::Idle)
+    , m_sensorReading(nullptr)
+    , m_sensorOptions(sensorOptions)
+{
+}
+
+// Getters
+String Sensor::state() const
+{
+    switch (m_sensorState) {
+    case SensorState::Idle:
+        return "idle";
+    case SensorState::Activating:
+        return "activating";
+    case SensorState::Active:
+        return "active";
+    case SensorState::Errored:
+        return "errored";
+    }
+    NOTREACHED();
+    return "idle";
+}
+
+SensorReading* Sensor::reading() const
+{
+    return m_sensorReading.get();
+}
+
+void Sensor::start(ScriptState* scriptState, ExceptionState& exceptionState)
+{
+
+    if (m_sensorState != SensorState::Idle && m_sensorState != SensorState::Errored) {
+        exceptionState.throwDOMException(InvalidStateError, "Invalid State: SensorState is not idle or errored");
+
+        m_hasEventListener = false;

[timvolodine, 2016/05/27 18:40:57]

Don't think this is needed? if sensor state is idle/errored m_hasEventListener
should have already been set accordignly and no need to call stopUpdating.

[riju_, 2016/05/30 10:15:13]

Done.

+        stopUpdating();
+        return;
+    }
+
+    updateState(SensorState::Activating);
+
+    // TODO(riju) : Add Permissions stuff later.
+
+    m_hasEventListener = true;
+    startUpdating();
+}
+
+void Sensor::stop(ScriptState* scriptState, ExceptionState& exceptionState)
+{
+    if (m_sensorState == SensorState::Idle || m_sensorState == SensorState::Errored) {
+        exceptionState.throwDOMException(InvalidStateError, "Invalid State: SensorState is either idle or errored");
+        return;
+    }
+
+    m_hasEventListener = false;
+    stopUpdating();
+
+    m_sensorReading.clear();
+    updateState(SensorState::Idle);
+}
+
+void Sensor::updateState(SensorState newState)
+{
+    DCHECK(isMainThread());
+    if (m_sensorState == newState)
+        return;
+
+    m_sensorState = newState;

[timvolodine, 2016/05/27 18:40:57]

Would be nice to have a state transitions check and some comments on the valid
transitions if that makes sense, like e.g. is done in AbstractAudioContext.cpp.
Could be done in a follow-up patch once the spec is clear on that. Maybe add a
TODO for this.

[riju_, 2016/05/30 10:15:13]

Done.

+    // Notify context that state changed
+    if (getExecutionContext())
+        getExecutionContext()->postTask(BLINK_FROM_HERE, createSameThreadTask(&Sensor::notifyStateChange, this));
+}
+
+void Sensor::notifyStateChange()
+{
+    dispatchEvent(Event::create(EventTypeNames::statechange));
+}
+
+void Sensor::suspend()
+{
+    m_hasEventListener = false;
+    stopUpdating();
+}
+
+void Sensor::resume()
+{
+    m_hasEventListener = true;
+    startUpdating();
+}
+
+void Sensor::stop()
+{
+    m_hasEventListener = false;
+    stopUpdating();
+}
+
+bool Sensor::hasPendingActivity() const
+{
+    // Prevent V8 from garbage collecting the wrapper object if there are
+    // event listeners attached to it.
+    return hasEventListeners();
+}
+
+DEFINE_TRACE(Sensor)
+{
+    ActiveDOMObject::trace(visitor);
+    EventTargetWithInlineData::trace(visitor);
+    PlatformEventController::trace(visitor);
+    visitor->trace(m_sensorReading);
+}
+
+} // namespace blink