Simplify line editor choice in d8.

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index 1c3ce0a122ec8bbe776f42332001ef81b77cdf3c..c26b7e0f22b22dd6a9a5eb8813299c75bb71d939 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -118,22 +118,14 @@ class CounterMap {
 
 class LineEditor {
  public:
-  enum Type { DUMB = 0, READLINE = 1 };
-  LineEditor(Type type, const char* name);
-  virtual ~LineEditor() { }
-
-  virtual Handle<String> Prompt(const char* prompt) = 0;
-  virtual bool Open() { return true; }
-  virtual bool Close() { return true; }
-  virtual void AddHistory(const char* str) { }
-
-  const char* name() { return name_; }
-  static LineEditor* Get();
+  explicit LineEditor(Isolate* isolate) : isolate_(isolate) { Open(); }
+  ~LineEditor();
+  void Open();
+  const char* name();
+  void AddHistory(const char* str);
+  Handle<String> Prompt(const char* prompt);
  private:
-  Type type_;
-  const char* name_;
-  LineEditor* next_;
-  static LineEditor* first_;
+  Isolate* isolate_;
 };