Update V8 to r6768 as required by WebKit r78450

Change-Id: Ib8868ff7147a76547a8d1d85f257ebe8546a3d3f
diff --git a/src/variables.h b/src/variables.h
index 882a52e..5d27a02 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -187,21 +187,23 @@
   Scope* scope_;
   Handle<String> name_;
   Mode mode_;
-  bool is_valid_LHS_;
   Kind kind_;
 
   Variable* local_if_not_shadowed_;
 
-  // Usage info.
-  bool is_accessed_from_inner_scope_;  // set by variable resolver
-  bool is_used_;
-
   // Static type information
   StaticType type_;
 
   // Code generation.
   // rewrite_ is usually a Slot or a Property, but may be any expression.
   Expression* rewrite_;
+
+  // Valid as a LHS? (const and this are not valid LHS, for example)
+  bool is_valid_LHS_;
+
+  // Usage info.
+  bool is_accessed_from_inner_scope_;  // set by variable resolver
+  bool is_used_;
 };