[date] Refactor the %_DateField intrinsic to be optimizable.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 30c35b1f0f93030caa07b4a8f69ddbfe1615fc55..9f068acf7cb732d6ce7d8215fe57c9f158411c8f 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -1794,11 +1794,6 @@ void LCodeGen::DoDateField(LDateField* instr) {
   DCHECK(object.is(result));
   DCHECK(object.is(eax));
 
-  __ test(object, Immediate(kSmiTagMask));
-  DeoptimizeIf(zero, instr, Deoptimizer::kSmi);
-  __ CmpObjectType(object, JS_DATE_TYPE, scratch);
-  DeoptimizeIf(not_equal, instr, Deoptimizer::kNotADateObject);
-
   if (index->value() == 0) {
     __ mov(result, FieldOperand(object, JSDate::kValueOffset));
   } else {