[Sensors] Fix reading updates after page refresh

third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.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/SensorReadingUpdater.h"
 
 #include "core/dom/Document.h"
 #include "device/generic_sensor/public/interfaces/sensor.mojom-blink.h"
 #include "modules/sensor/SensorProxy.h"
 #include "wtf/CurrentTime.h"
 
 using device::mojom::blink::ReportingMode;
 
 namespace blink {
 
 SensorReadingUpdater::SensorReadingUpdater(SensorProxy* sensorProxy)
-    : m_sensorProxy(sensorProxy), m_hasPendingAnimationFrameTask(false) {}
+    : m_sensorProxy(sensorProxy),
+      m_document(m_sensorProxy->document()),
+      m_hasPendingAnimationFrameTask(false) {}
 
 void SensorReadingUpdater::enqueueAnimationFrameTask() {
+  if (!m_document || m_document->isDetached()) {
+    // If the document has detached the scheduled callbacks
+    // will never be called.
+    m_hasPendingAnimationFrameTask = false;
+    m_document = m_sensorProxy->document();
+    if (!m_document)

[haraken, 2017/01/27 11:30:33]

Don't you need to add '|| m_document->isDetached()'?

+      return;
+  }
+
   if (m_hasPendingAnimationFrameTask)
     return;
 
   auto callback = WTF::bind(&SensorReadingUpdater::onAnimationFrame,
                             wrapWeakPersistent(this));
-  m_sensorProxy->document()->enqueueAnimationFrameTask(std::move(callback));
+  m_document->enqueueAnimationFrameTask(std::move(callback));

[haraken, 2017/01/26 22:24:14]

A final question: Why do you need m_document in the first place? Can we do
something like this?

if (m_sensorProxy->document() && !m_sensorProxy->document()->isDetached()) {
  m_sensorProxy->document()->enqueueAnimationFrameTask(...);
}

   m_hasPendingAnimationFrameTask = true;
 }
 
 void SensorReadingUpdater::start() {
   enqueueAnimationFrameTask();
 }
 
 void SensorReadingUpdater::onAnimationFrame() {
   m_hasPendingAnimationFrameTask = false;
   onAnimationFrameInternal();
 }
 
 DEFINE_TRACE(SensorReadingUpdater) {
+  visitor->trace(m_document);
   visitor->trace(m_sensorProxy);
 }
 
 class SensorReadingUpdaterContinuous : public SensorReadingUpdater {
  public:
   explicit SensorReadingUpdaterContinuous(SensorProxy* sensorProxy)
       : SensorReadingUpdater(sensorProxy) {}
 
   DEFINE_INLINE_VIRTUAL_TRACE() { SensorReadingUpdater::trace(visitor); }
 
@@ skipping 54 matching lines @@
 
 // static
 SensorReadingUpdater* SensorReadingUpdater::create(SensorProxy* proxy,
                                                    ReportingMode mode) {
   if (mode == ReportingMode::CONTINUOUS)
     return new SensorReadingUpdaterContinuous(proxy);
   return new SensorReadingUpdaterOnChange(proxy);
 }
 
 }  // namespace blink