[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..7660de6b7b7ed2524231e1f04c8f4970e74e23ac 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_sensorProxy->document()) {

[haraken, 2017/01/24 21:19:14]

This condition doesn't look correct to me.

Note that WeakMember is cleared only when a GC is triggered; i.e., it doesn't
get cleared until you hit a next GC.

I think what you want to do here is:

- Make SensorProxy (or SensorReadingUpdater) inherit from ContextClient
- Then SensorProxy::getExecutionContext() returns false after the Document is
detached. You can use it to check if the Document is detached or not.

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