X87: Fix issue with __proto__ when using ES6 object literals.

port bc3b2960 (r26172).

original commit message:
  Fix issue with __proto__ when using ES6 object literals

  It should be possible to create a concise method with the name
  __proto__ without setting the [[Prototype]]. Similarly, property
  name shorthands with the name __proto__ should define an own
  property.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/856313002

Cr-Commit-Position: refs/heads/master@{#26179}

src/x87/full-codegen-x87.cc

@@ -2456,8 +2456,9 @@ void FullCodeGenerator::EmitClassDefineProperties(ClassLiteral* lit) {
     switch (property->kind()) {
       case ObjectLiteral::Property::CONSTANT:
       case ObjectLiteral::Property::MATERIALIZED_LITERAL:
-      case ObjectLiteral::Property::COMPUTED:
       case ObjectLiteral::Property::PROTOTYPE:
+        UNREACHABLE();
+      case ObjectLiteral::Property::COMPUTED:
         __ CallRuntime(Runtime::kDefineClassMethod, 3);
         break;
 
@@ -2468,9 +2469,6 @@ void FullCodeGenerator::EmitClassDefineProperties(ClassLiteral* lit) {
       case ObjectLiteral::Property::SETTER:
         __ CallRuntime(Runtime::kDefineSetterPropertyUnchecked, 3);
         break;
-
-      default:
-        UNREACHABLE();
     }
   }