Minimize malloc heap allocation on process startup.

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index 5024bce63ff22de0fd4a172b0944c5a4bd5d15df..2d58ce1f54aefba1e93be618b9a1f76a69f7bcd3 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -1965,7 +1965,7 @@ void Debug::AfterGarbageCollection() {
 
 
 Debugger::Debugger(Isolate* isolate)
-    : debugger_access_(OS::CreateMutex()),
+    : debugger_access_(isolate->debugger_access()),
       event_listener_(Handle<Object>()),
       event_listener_data_(Handle<Object>()),
       compiling_natives_(false),
@@ -1987,8 +1987,6 @@ Debugger::Debugger(Isolate* isolate)
 
 
 Debugger::~Debugger() {
-  delete debugger_access_;
-  debugger_access_ = 0;
   delete dispatch_handler_access_;
   dispatch_handler_access_ = 0;
   delete command_received_;