Don't run the second pass of the pending phantom callbacks if the heap has been torn down.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 42e22b4fd248b263a9de051da6f7ad6b73276339..c84b8b9f9286f64604ab97b4cc4e01e2625738ff 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -6,11 +6,14 @@
 #define V8_ISOLATE_H_
 
 #include <queue>
+#include <set>
+
 #include "include/v8-debug.h"
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/base/atomicops.h"
 #include "src/builtins.h"
+#include "src/cancelable-task.h"
 #include "src/contexts.h"
 #include "src/date.h"
 #include "src/execution.h"
@@ -1133,6 +1136,9 @@ class Isolate {
 
   FutexWaitListNode* futex_wait_list_node() { return &futex_wait_list_node_; }
 
+  void RegisterCancelableTask(CancelableTask* task);
+  void RemoveCancelableTask(CancelableTask* task);
+
  protected:
   explicit Isolate(bool enable_serializer);
 
@@ -1368,6 +1374,8 @@ class Isolate {
 
   FutexWaitListNode futex_wait_list_node_;
 
+  std::set<CancelableTask*> cancelable_tasks_;
+
   friend class ExecutionAccess;
   friend class HandleScopeImplementer;
   friend class OptimizingCompileDispatcher;