Simplify implementation of Mutex.

src/optimizing-compiler-thread.h

Index: src/optimizing-compiler-thread.h
diff --git a/src/optimizing-compiler-thread.h b/src/optimizing-compiler-thread.h
index 275ceb40b711ccecf4ee4937355fed1eb8f23c61..336522fb2789480985ec58a69b094a142ce0ea48 100644
--- a/src/optimizing-compiler-thread.h
+++ b/src/optimizing-compiler-thread.h
@@ -46,12 +46,10 @@ class OptimizingCompilerThread : public Thread {
       Thread("OptimizingCompilerThread"),
 #ifdef DEBUG
       thread_id_(0),
-      thread_id_mutex_(OS::CreateMutex()),
 #endif
       isolate_(isolate),
       stop_semaphore_(OS::CreateSemaphore(0)),
       input_queue_semaphore_(OS::CreateSemaphore(0)),
-      install_mutex_(OS::CreateMutex()),
       time_spent_compiling_(0),
       time_spent_total_(0) {
     NoBarrier_Store(&stop_thread_, static_cast<AtomicWord>(false));
@@ -83,18 +81,14 @@ class OptimizingCompilerThread : public Thread {
 #endif
 
   ~OptimizingCompilerThread() {
-    delete install_mutex_;
     delete input_queue_semaphore_;
     delete stop_semaphore_;
-#ifdef DEBUG
-    delete thread_id_mutex_;
-#endif
   }
 
  private:
 #ifdef DEBUG
   int thread_id_;
-  Mutex* thread_id_mutex_;
+  Mutex thread_id_mutex_;
 #endif
 
   Isolate* isolate_;
@@ -102,7 +96,7 @@ class OptimizingCompilerThread : public Thread {
   Semaphore* input_queue_semaphore_;
   UnboundQueue<OptimizingCompiler*> input_queue_;
   UnboundQueue<OptimizingCompiler*> output_queue_;
-  Mutex* install_mutex_;
+  Mutex install_mutex_;
   volatile AtomicWord stop_thread_;
   volatile Atomic32 queue_length_;
   int64_t time_spent_compiling_;