Introduce extended mode.

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index f85f286b38bf5dfbf0961dba271cc97fab98a6aa..63c1e73bea832f513ef2438773effbc5b4251927 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -361,7 +361,30 @@ template <typename T, class P = FreeStoreAllocationPolicy> class List;
 // -----------------------------------------------------------------------------
 // Declarations for use in both the preparser and the rest of V8.
 
+// The different language modes that V8 implements. ES5 defines two language
+// modes: an unrestricted mode respectively a strict mode which are indicated by
+// CLASSIC_MODE respectively STRICT_MODE in the enum. The harmony spec drafts
+// for the next ES standard specify a new third mode which is called 'extended
+// mode'. The extended mode is only available if the harmony flag is set. It is
+// based on the 'strict mode' and adds new functionality to it. This means that
+// most of the semantics of these two modes coincide.
+//
+// In the current draft the term 'base code' is used to refer to code that is
+// neither in strict nor extended mode. However, the more distinguishing term
+// 'classic mode' is used in V8 instead to avoid mix-ups.
+
+enum LanguageMode {
+  CLASSIC_MODE,
+  STRICT_MODE,
+  EXTENDED_MODE
+};
+
+
 // The Strict Mode (ECMA-262 5th edition, 4.2.2).
+//
+// This flag is used in the backend to represent the language mode. So far
+// there is no semantic difference between the strict and the extended mode in
+// the backend, so both modes are represented by the kStrictMode value.
 enum StrictModeFlag {
   kNonStrictMode,
   kStrictMode