Oilpan: Don't destruct HRTFDatabaseLoader::m_thread during a sweeping phase

Source/platform/audio/HRTFDatabaseLoader.h

Index: Source/platform/audio/HRTFDatabaseLoader.h
diff --git a/Source/platform/audio/HRTFDatabaseLoader.h b/Source/platform/audio/HRTFDatabaseLoader.h
index 74408b2cf76efdf53acb8ca1eae4dffafdcbe8b1..fcdd1a6d1336e4769793cfbdcfa56988dcdd92d2 100644
--- a/Source/platform/audio/HRTFDatabaseLoader.h
+++ b/Source/platform/audio/HRTFDatabaseLoader.h
@@ -37,6 +37,8 @@
 
 namespace blink {
 
+class TaskSynchronizer;
+
 // HRTFDatabaseLoader will asynchronously load the default HRTFDatabase in a new thread.
 
 class PLATFORM_EXPORT HRTFDatabaseLoader final : public GarbageCollectedFinalized<HRTFDatabaseLoader> {
@@ -60,9 +62,6 @@ public:
 
     float databaseSampleRate() const { return m_databaseSampleRate; }
 
-    // Called in asynchronous loading thread.
-    void load();
-
     void trace(Visitor*) { }
 
 private:
@@ -73,6 +72,10 @@ private:
     // This must be called from the main thread.
     void loadAsynchronously();
 
+    // Called in asynchronous loading thread.
+    void loadTask();
+    void cleanupTask(TaskSynchronizer*);
+
     // Holding a m_lock is required when accessing m_hrtfDatabase since we access it from multiple threads.
     Mutex m_lock;
     OwnPtr<HRTFDatabase> m_hrtfDatabase;