Add AssertSmi() in x64 MacroAssembler::SmiTest().

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/19647006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15790 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/macro-assembler-x64.cc

@@ -1158,6 +1158,7 @@ void MacroAssembler::SmiToInteger64(Register dst, const Operand& src) {
 
 
 void MacroAssembler::SmiTest(Register src) {
+  AssertSmi(src);
   testq(src, src);
 }