Simplify implementation of Mutex.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index c0083177373e0afcd5f899cb92d46e236936dd59..009ff78ed1033eb9613df95ce6c8da4d7b6db440 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -544,10 +544,10 @@ class Isolate {
   static void EnterDefaultIsolate();
 
   // Mutex for serializing access to break control structures.
-  Mutex* break_access() { return break_access_; }
+  Mutex* break_access() { return &break_access_; }
 
   // Mutex for serializing access to debugger.
-  Mutex* debugger_access() { return debugger_access_; }
+  Mutex* debugger_access() { return &debugger_access_; }
 
   Address get_address_from_id(AddressId id);
 
@@ -1200,7 +1200,7 @@ class Isolate {
 
   // This mutex protects highest_thread_id_, thread_data_table_ and
   // default_isolate_.
-  static Mutex* process_wide_mutex_;
+  static Mutex process_wide_mutex_;
 
   static Thread::LocalStorageKey per_isolate_thread_data_key_;
   static Thread::LocalStorageKey isolate_key_;
@@ -1268,9 +1268,9 @@ class Isolate {
   CompilationCache* compilation_cache_;
   Counters* counters_;
   CodeRange* code_range_;
-  Mutex* break_access_;
+  Mutex break_access_;
   Atomic32 debugger_initialized_;
-  Mutex* debugger_access_;
+  Mutex debugger_access_;
   Logger* logger_;
   StackGuard stack_guard_;
   StatsTable* stats_table_;
@@ -1462,11 +1462,11 @@ class ExecutionAccess BASE_EMBEDDED {
   }
   ~ExecutionAccess() { Unlock(isolate_); }
 
-  static void Lock(Isolate* isolate) { isolate->break_access_->Lock(); }
-  static void Unlock(Isolate* isolate) { isolate->break_access_->Unlock(); }
+  static void Lock(Isolate* isolate) { isolate->break_access()->Lock(); }
+  static void Unlock(Isolate* isolate) { isolate->break_access()->Unlock(); }
 
   static bool TryLock(Isolate* isolate) {
-    return isolate->break_access_->TryLock();
+    return isolate->break_access()->TryLock();
   }
 
  private: