Retire StringTracker.

src/api.h

Index: src/api.h
diff --git a/src/api.h b/src/api.h
index 438c4f31dc40967df0208c8ba518f6d83297d077..fc7a4eff6fc85992ced1c8329471c99d73be1063 100644
--- a/src/api.h
+++ b/src/api.h
@@ -406,72 +406,6 @@ OPEN_HANDLE_LIST(MAKE_OPEN_HANDLE)
 
 namespace internal {
 
-// Tracks string usage to help make better decisions when
-// externalizing strings.
-//
-// Implementation note: internally this class only tracks fresh
-// strings and keeps a single use counter for them.
-class StringTracker {
- public:
-  // Records that the given string's characters were copied to some
-  // external buffer. If this happens often we should honor
-  // externalization requests for the string.
-  void RecordWrite(Handle<String> string) {
-    Address address = reinterpret_cast<Address>(*string);
-    Address top = isolate_->heap()->NewSpaceTop();
-    if (IsFreshString(address, top)) {
-      IncrementUseCount(top);
-    }
-  }
-
-  // Estimates freshness and use frequency of the given string based
-  // on how close it is to the new space top and the recorded usage
-  // history.
-  inline bool IsFreshUnusedString(Handle<String> string) {
-    Address address = reinterpret_cast<Address>(*string);
-    Address top = isolate_->heap()->NewSpaceTop();
-    return IsFreshString(address, top) && IsUseCountLow(top);
-  }
-
- private:
-  StringTracker() : use_count_(0), last_top_(NULL), isolate_(NULL) { }
-
-  static inline bool IsFreshString(Address string, Address top) {
-    return top - kFreshnessLimit <= string && string <= top;
-  }
-
-  inline bool IsUseCountLow(Address top) {
-    if (last_top_ != top) return true;
-    return use_count_ < kUseLimit;
-  }
-
-  inline void IncrementUseCount(Address top) {
-    if (last_top_ != top) {
-      use_count_ = 0;
-      last_top_ = top;
-    }
-    ++use_count_;
-  }
-
-  // Single use counter shared by all fresh strings.
-  int use_count_;
-
-  // Last new space top when the use count above was valid.
-  Address last_top_;
-
-  Isolate* isolate_;
-
-  // How close to the new space top a fresh string has to be.
-  static const int kFreshnessLimit = 1024;
-
-  // The number of uses required to consider a string useful.
-  static const int kUseLimit = 32;
-
-  friend class Isolate;
-
-  DISALLOW_COPY_AND_ASSIGN(StringTracker);
-};
-
 
 class DeferredHandles {
  public: