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

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 3c845cba296438883f75633af7084410e9528df4..e4f03946007a6807de13fb1e502e9d4985c6ed29 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1936,11 +1936,6 @@ void LCodeGen::DoDateField(LDateField* instr) {
   DCHECK(!scratch.is(scratch0()));
   DCHECK(!scratch.is(object));
 
-  __ SmiTst(object);
-  DeoptimizeIf(eq, instr, Deoptimizer::kSmi);
-  __ CompareObjectType(object, scratch, scratch, JS_DATE_TYPE);
-  DeoptimizeIf(ne, instr, Deoptimizer::kNotADateObject);
-
   if (index->value() == 0) {
     __ ldr(result, FieldMemOperand(object, JSDate::kValueOffset));
   } else {