Reland "Disable the CompilerDispatcher if we don't have idle time"

src/compiler-dispatcher/compiler-dispatcher.h

Index: src/compiler-dispatcher/compiler-dispatcher.h
diff --git a/src/compiler-dispatcher/compiler-dispatcher.h b/src/compiler-dispatcher/compiler-dispatcher.h
index 220fcd0596c2e0035b6b267681ed7ec5dbf09f43..fea141e22f970ff9112290707539ca5d4c574015 100644
--- a/src/compiler-dispatcher/compiler-dispatcher.h
+++ b/src/compiler-dispatcher/compiler-dispatcher.h
@@ -61,6 +61,7 @@ class V8_EXPORT_PRIVATE CompilerDispatcher {
       JobMap;
   class IdleTask;
 
+  bool IsEnabled() const;
   JobMap::const_iterator GetJobFor(Handle<SharedFunctionInfo> shared) const;
   void ScheduleIdleTaskIfNeeded();
   void DoIdleWork(double deadline_in_seconds);