Implement code stub for object literal creation.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 35b902d7aea8539f5de3251b42d5adc9e156decf..728f1813d5434e2d52c204316c0eeb2c489773cb 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1376,10 +1376,11 @@ void FullCodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
 
 void FullCodeGenerator::VisitObjectLiteral(ObjectLiteral* expr) {
   Comment cmnt(masm_, "[ ObjectLiteral");
+  Handle<FixedArray> constant_properties = expr->constant_properties();
   __ movq(rdi, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
   __ push(FieldOperand(rdi, JSFunction::kLiteralsOffset));
   __ Push(Smi::FromInt(expr->literal_index()));
-  __ Push(expr->constant_properties());
+  __ Push(constant_properties);
   int flags = expr->fast_elements()
       ? ObjectLiteral::kFastElements
       : ObjectLiteral::kNoFlags;
@@ -1387,10 +1388,15 @@ void FullCodeGenerator::VisitObjectLiteral(ObjectLiteral* expr) {
       ? ObjectLiteral::kHasFunction
       : ObjectLiteral::kNoFlags;
   __ Push(Smi::FromInt(flags));
+  int properties_count = constant_properties->length() / 2;
   if (expr->depth() > 1) {
     __ CallRuntime(Runtime::kCreateObjectLiteral, 4);
-  } else {
+  } else if (flags != ObjectLiteral::kFastElements ||
+      properties_count > FastCloneShallowObjectStub::kMaximumClonedProperties) {
     __ CallRuntime(Runtime::kCreateObjectLiteralShallow, 4);
+  } else {
+    FastCloneShallowObjectStub stub(properties_count);
+    __ CallStub(&stub);
   }
 
   // If result_saved is true the result is on top of the stack.  If