Make Variable::is_this always return the correct value

src/full-codegen/x87/full-codegen-x87.cc

Index: src/full-codegen/x87/full-codegen-x87.cc
diff --git a/src/full-codegen/x87/full-codegen-x87.cc b/src/full-codegen/x87/full-codegen-x87.cc
index 7aa837259d5c8c68159b3ce2bda69512b8b2e345..33d0c83bc055ae801c23dc002877d6e2175327d7 100644
--- a/src/full-codegen/x87/full-codegen-x87.cc
+++ b/src/full-codegen/x87/full-codegen-x87.cc
@@ -2946,7 +2946,7 @@ void FullCodeGenerator::VisitUnaryOperation(UnaryOperation* expr) {
         Variable* var = proxy->var();
         // Delete of an unqualified identifier is disallowed in strict mode but
         // "delete this" is allowed.
-        bool is_this = var->HasThisName(isolate());
+        bool is_this = var->is_this();
         DCHECK(is_sloppy(language_mode()) || is_this);
         if (var->IsUnallocatedOrGlobalSlot()) {
           __ mov(eax, NativeContextOperand());