Use idle task to perform incremental marking steps.

src/v8.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_V8_H_
 #define V8_V8_H_
 
 #include "include/v8.h"
 #include "src/allocation.h"
 
 namespace v8 {
 namespace internal {
 
 class V8 : public AllStatic {
  public:
   // Global actions.
 
   static bool Initialize();
   static void TearDown();
 
   // Report process out of memory. Implementation found in api.cc.
   // This function will not return, but will terminate the execution.
   static void FatalProcessOutOfMemory(const char* location,
                                       bool take_snapshot = false);
 
   static void InitializePlatform(v8::Platform* platform);
   static void ShutdownPlatform();
   static v8::Platform* GetCurrentPlatform();
+  // Replaces the current platform with the given platform.
+  // Should be used only for testing.
+  static void SetPlatformForTesting(v8::Platform* platform);
 
   static void SetNativesBlob(StartupData* natives_blob);
   static void SetSnapshotBlob(StartupData* snapshot_blob);
 
  private:
   static void InitializeOncePerProcessImpl();
   static void InitializeOncePerProcess();
 
   // v8::Platform to use.
   static v8::Platform* platform_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8_H_