Move MainThreadTaskRunner off Oilpan heap to simplify posting.

third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp

Index: third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp
diff --git a/third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp b/third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp
index 4baf2bb94f13f155fc51ff676c29b0b9de58b08c..8ede5dfa62327d647d38e5879684efd9f3ee6a1a 100644
--- a/third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp
+++ b/third_party/WebKit/Source/core/dom/MainThreadTaskRunner.cpp
@@ -39,6 +39,7 @@ MainThreadTaskRunner::MainThreadTaskRunner(ExecutionContext* context)
     : m_context(context)
     , m_pendingTasksTimer(this, &MainThreadTaskRunner::pendingTasksTimerFired)
     , m_suspended(false)
+    , m_weakFactory(this)
 {
 }
 
@@ -46,16 +47,11 @@ MainThreadTaskRunner::~MainThreadTaskRunner()
 {
 }
 
-DEFINE_TRACE(MainThreadTaskRunner)
-{
-    visitor->trace(m_context);
-}
-
 void MainThreadTaskRunner::postTaskInternal(const WebTraceLocation& location, PassOwnPtr<ExecutionContextTask> task, bool isInspectorTask)
 {
     Platform::current()->mainThread()->getWebTaskRunner()->postTask(location, threadSafeBind(
         &MainThreadTaskRunner::perform,
-        CrossThreadWeakPersistentThisPointer<MainThreadTaskRunner>(this),
+        AllowCrossThreadAccess(m_weakFactory.createWeakPtr()),
         passed(std::move(task)),
         isInspectorTask));
 }
@@ -74,6 +70,11 @@ void MainThreadTaskRunner::postInspectorTask(const WebTraceLocation& location, P
 
 void MainThreadTaskRunner::perform(PassOwnPtr<ExecutionContextTask> task, bool isInspectorTask)
 {
+    // If the owner m_context is about to be swept then it
+    // is no longer safe to access.
+    if (ThreadHeap::willObjectBeLazilySwept(m_context.get()))

[haraken, 2016/05/04 03:21:33]

Why was this check not needed before this CL?

[sof, 2016/05/04 05:17:39]

The closure is constructed using
CrossThreadWeakPersistentThisPointer<MainThreadTaskRunner>(this) and
MainThreadTaskRunner & Document die at the same time, so no need to separately
check the liveness of m_context here.

+        return;
+
     if (!isInspectorTask && (m_context->tasksNeedSuspension() || !m_pendingTasks.isEmpty())) {
         m_pendingTasks.append(std::move(task));
         return;
@@ -101,6 +102,11 @@ void MainThreadTaskRunner::resume()
 
 void MainThreadTaskRunner::pendingTasksTimerFired(Timer<MainThreadTaskRunner>*)
 {
+    // If the owner m_context is about to be swept then it
+    // is no longer safe to access.
+    if (ThreadHeap::willObjectBeLazilySwept(m_context.get()))
+        return;
+
     while (!m_pendingTasks.isEmpty()) {
         OwnPtr<ExecutionContextTask> task = m_pendingTasks[0].release();
         m_pendingTasks.remove(0);