Inline single test-only call of Scope::LookupThis method

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 6c976d90bd666f533381dd419a2cba97abcac110..71d1129b2bd649351e79d519acebf46d3a666af1 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -386,8 +386,6 @@ class Scope: public ZoneObject {
     return receiver_;
   }
 
-  Variable* LookupThis() { return Lookup(ast_value_factory_->this_string()); }
-
   // TODO(wingo): Add a GLOBAL_SCOPE scope type which will lexically allocate
   // "this" (and no other variable) on the native context.  Script scopes then
   // will not have a "this" declaration.