Fix invalid SMI test in x64 ToNumberStub::Generate().

TBR=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/19927002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15788 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/code-stubs-x64.cc

@@ -299,8 +299,7 @@ void HydrogenCodeStub::GenerateLightweightMiss(MacroAssembler* masm) {
 void ToNumberStub::Generate(MacroAssembler* masm) {
   // The ToNumber stub takes one argument in rax.
   Label check_heap_number, call_builtin;
-  __ SmiTest(rax);
-  __ j(not_zero, &check_heap_number, Label::kNear);
+  __ JumpIfNotSmi(rax, &check_heap_number, Label::kNear);
   __ Ret();
 
   __ bind(&check_heap_number);