Introduce LanguageMode, drop StrictMode.

src/full-codegen.h

Index: src/full-codegen.h
diff --git a/src/full-codegen.h b/src/full-codegen.h
index 2c12da4c2c66e12956574fc68150b5d2602eb853..ce691c37e19f88806e3b2c72db419f4b51535c9a 100644
--- a/src/full-codegen.h
+++ b/src/full-codegen.h
@@ -603,11 +603,11 @@ class FullCodeGenerator: public AstVisitor {
   // Shall an error be thrown if assignment with 'op' operation is perfomed
   // on this variable in given language mode?
   static bool IsSignallingAssignmentToConst(Variable* var, Token::Value op,
-                                            StrictMode strict_mode) {
+                                            LanguageMode language_mode) {
     if (var->mode() == CONST) return op != Token::INIT_CONST;
 
     if (var->mode() == CONST_LEGACY) {
-      return strict_mode == STRICT && op != Token::INIT_CONST_LEGACY;
+      return is_strict(language_mode) && op != Token::INIT_CONST_LEGACY;
     }
 
     return false;
@@ -686,7 +686,7 @@ class FullCodeGenerator: public AstVisitor {
   Handle<Script> script() { return info_->script(); }
   bool is_eval() { return info_->is_eval(); }
   bool is_native() { return info_->is_native(); }
-  StrictMode strict_mode() { return function()->strict_mode(); }
+  LanguageMode language_mode() { return function()->language_mode(); }
   FunctionLiteral* function() { return info_->function(); }
   Scope* scope() { return scope_; }