Add script context with context-allocated "const this"

src/variables.h

Index: src/variables.h
diff --git a/src/variables.h b/src/variables.h
index 0cb50c87e985580c1fd1c7fc5ea9b3fde63f4206..218eefae08e08a0cd937a14e1d158c5b878d1a0c 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -105,6 +105,16 @@ class Variable: public ZoneObject {
   bool is_this() const { return kind_ == THIS; }
   bool is_arguments() const { return kind_ == ARGUMENTS; }
 
+  // For script scopes, the "this" binding is provided by a ScriptContext added
+  // to the global's ScriptContextTable.  This binding might not statically
+  // resolve to a Variable::THIS binding, instead being DYNAMIC_LOCAL.  However
+  // any variable named "this" does indeed refer to a Variable::THIS binding;
+  // the grammar ensures this to be the case.  So wherever a "this" binding
+  // might be provided by the global, use HasThisName instead of is_this().
+  bool HasThisName(Isolate* isolate) const {
+    return is_this() || *name() == *isolate->factory()->this_string();
+  }
+
   ClassVariable* AsClassVariable() {
     DCHECK(is_class());
     return reinterpret_cast<ClassVariable*>(this);