[Sensors] Fix reading updates after page refresh

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

Index: third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.cpp
diff --git a/third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.cpp b/third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.cpp
index 3d35f7da1f8c0a31755ddbe5f2056c1113818b68..0c938d16ce544fa9694dba4f7719ebe81db9e0de 100644
--- a/third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.cpp
+++ b/third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.cpp
@@ -17,12 +17,21 @@ SensorReadingUpdater::SensorReadingUpdater(SensorProxy* sensorProxy)
     : m_sensorProxy(sensorProxy), m_hasPendingAnimationFrameTask(false) {}
 
 void SensorReadingUpdater::enqueueAnimationFrameTask() {
+  if (!m_document || m_document->isDetached()) {

[haraken, 2017/01/25 18:20:06]

Will the following work?

- Make SensorReadingUpdater inherit from ContextClient
- Use if(!getExecutionContext()) here.

[Mikhail, 2017/01/26 06:19:59]

As far as I see, ContextClient contains ExecutionContext instance which can be
set only once at construction, so inheriting from it would require re-creation
of the SensorReadingUpdater instance every time the context is detached,
further, we'd need to introduce a notification mechanism (or just a similar
SensorReadingUpdater  state checking) on the upper level to be aware if the
current SensorReadingUpdater instance must be re-created.
Considering all above the current approach IMO looks simpler.

+    // If the document has detached the scheduled callbacks
+    // will never be called.
+    m_hasPendingAnimationFrameTask = false;
+    m_document = m_sensorProxy->document();

[haraken, 2017/01/25 18:20:06]

Can we set m_document in SensorReadingUpdater's constructor?

Once you make SensorReadingUpdater inherit from ContextClient, it won't be
needed though.

[Mikhail, 2017/01/26 06:19:59]

Done.

+    if (!m_document)
+      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));
   m_hasPendingAnimationFrameTask = true;
 }
 
@@ -36,6 +45,7 @@ void SensorReadingUpdater::onAnimationFrame() {
 }
 
 DEFINE_TRACE(SensorReadingUpdater) {
+  visitor->trace(m_document);
   visitor->trace(m_sensorProxy);
 }