Add CancelableIdleTask.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 585c5b8bf2f5f54bb3013bdcdff0538c12318c64..a11f75ab290a1ce82439fa89c5508f3167e567bb 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1139,8 +1139,8 @@ class Isolate {
 
   FutexWaitListNode* futex_wait_list_node() { return &futex_wait_list_node_; }
 
-  void RegisterCancelableTask(CancelableTask* task);
-  void RemoveCancelableTask(CancelableTask* task);
+  void RegisterCancelableTask(Cancelable* task);
+  void RemoveCancelableTask(Cancelable* task);
 
  protected:
   explicit Isolate(bool enable_serializer);
@@ -1379,7 +1379,7 @@ class Isolate {
 
   FutexWaitListNode futex_wait_list_node_;
 
-  std::set<CancelableTask*> cancelable_tasks_;
+  std::set<Cancelable*> cancelable_tasks_;
 
   friend class ExecutionAccess;
   friend class HandleScopeImplementer;