Reland "Use background tasks for the compiler dispatcher

src/cancelable-task.h

Index: src/cancelable-task.h
diff --git a/src/cancelable-task.h b/src/cancelable-task.h
index 65f98e766287dea41bb89ec2f1e02cdc65242df4..578db6f6b997c624a0c3a7af901978f6fd534de7 100644
--- a/src/cancelable-task.h
+++ b/src/cancelable-task.h
@@ -126,6 +126,7 @@ class V8_EXPORT_PRIVATE Cancelable {
 class CancelableTask : public Cancelable, public Task {
  public:
   explicit CancelableTask(Isolate* isolate);
+  CancelableTask(Isolate* isolate, CancelableTaskManager* manager);
 
   // Task overrides.
   void Run() final {
@@ -148,6 +149,7 @@ class CancelableTask : public Cancelable, public Task {
 class CancelableIdleTask : public Cancelable, public IdleTask {
  public:
   explicit CancelableIdleTask(Isolate* isolate);
+  CancelableIdleTask(Isolate* isolate, CancelableTaskManager* manager);
 
   // IdleTask overrides.
   void Run(double deadline_in_seconds) final {