Implement IsNullCheck for CheckClassInstr. If input is nullable expected type, then check for null …

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 25902)
+++ runtime/vm/object.cc	(working copy)
@@ -9252,12 +9252,20 @@
   ASSERT(target != NULL);
   ASSERT(num_args_tested() == 1);
   const Array& data = Array::Handle(ic_data());
-  intptr_t data_pos = index * TestEntryLength();
+  const intptr_t data_pos = index * TestEntryLength();
   *class_id = Smi::Value(Smi::RawCast(data.At(data_pos)));
   *target ^= data.At(data_pos + 1);
 }
 
 
+intptr_t ICData::GetCidAt(intptr_t index) const {
+  ASSERT(num_args_tested() == 1);
+  const Array& data = Array::Handle(ic_data());
+  const intptr_t data_pos = index * TestEntryLength();
+  return Smi::Value(Smi::RawCast(data.At(data_pos)));
+}
+
+
 intptr_t ICData::GetClassIdAt(intptr_t index, intptr_t arg_nr) const {
   GrowableArray<intptr_t> class_ids;
   Function& target = Function::Handle();