Make idle tasks optional in the default platform.

src/libplatform/default-platform.h

Index: src/libplatform/default-platform.h
diff --git a/src/libplatform/default-platform.h b/src/libplatform/default-platform.h
index 0ab8e33ee5574ee55085accffda5011da00e990a..25d161a3bd2450f1e30e44648fa04aa8a18f2076 100644
--- a/src/libplatform/default-platform.h
+++ b/src/libplatform/default-platform.h
@@ -12,6 +12,7 @@
 #include <vector>
 
 #include "include/libplatform/libplatform-export.h"
+#include "include/libplatform/libplatform.h"
 #include "include/libplatform/v8-tracing.h"
 #include "include/v8-platform.h"
 #include "src/base/compiler-specific.h"
@@ -32,7 +33,8 @@ class TracingController;
 
 class V8_PLATFORM_EXPORT DefaultPlatform : public NON_EXPORTED_BASE(Platform) {
  public:
-  DefaultPlatform();
+  explicit DefaultPlatform(
+      IdleTaskSupport idle_task_support = IdleTaskSupport::kDisabled);
   virtual ~DefaultPlatform();
 
   void SetThreadPoolSize(int thread_pool_size);
@@ -81,6 +83,7 @@ class V8_PLATFORM_EXPORT DefaultPlatform : public NON_EXPORTED_BASE(Platform) {
   base::Mutex lock_;
   bool initialized_;
   int thread_pool_size_;
+  IdleTaskSupport idle_task_support_;
   std::vector<WorkerThread*> thread_pool_;
   TaskQueue queue_;
   std::map<v8::Isolate*, std::queue<Task*>> main_thread_queue_;