Retire StringTracker.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index ccbeadc79c920f01c170bba2503f5756d8497ad6..f5d6bc955884acc3e7c3c83501f79b9a4c6a37d3 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1760,7 +1760,6 @@ Isolate::Isolate(bool enable_serializer)
       eternal_handles_(NULL),
       thread_manager_(NULL),
       has_installed_extensions_(false),
-      string_tracker_(NULL),
       regexp_stack_(NULL),
       date_cache_(NULL),
       call_descriptor_data_(NULL),
@@ -1995,9 +1994,6 @@ Isolate::~Isolate() {
   delete thread_manager_;
   thread_manager_ = NULL;
 
-  delete string_tracker_;
-  string_tracker_ = NULL;
-
   delete memory_allocator_;
   memory_allocator_ = NULL;
   delete code_range_;
@@ -2104,8 +2100,6 @@ bool Isolate::Init(Deserializer* des) {
   FOR_EACH_ISOLATE_ADDRESS_NAME(ASSIGN_ELEMENT)
 #undef ASSIGN_ELEMENT
 
-  string_tracker_ = new StringTracker();
-  string_tracker_->isolate_ = this;
   compilation_cache_ = new CompilationCache(this);
   keyed_lookup_cache_ = new KeyedLookupCache();
   context_slot_cache_ = new ContextSlotCache();