Use off-heap data for class check instructions

runtime/vm/assembler_arm64.h

Index: runtime/vm/assembler_arm64.h
diff --git a/runtime/vm/assembler_arm64.h b/runtime/vm/assembler_arm64.h
index 200ec84b2fa6a643154e0570e9ece62ad68ea369..e50ca34efef58fa9b08d3fc86d020b9270a6b949 100644
--- a/runtime/vm/assembler_arm64.h
+++ b/runtime/vm/assembler_arm64.h
@@ -1144,6 +1144,11 @@ class Assembler : public ValueObject {
     b(label, NE);
   }
 
+  void BranchIfSmi(Register reg, Label* label) {
+    tsti(reg, Immediate(kSmiTagMask));
+    b(label, EQ);
+  }
+
   void Branch(const StubEntry& stub_entry,
               Register pp,
               Patchability patchable = kNotPatchable);
@@ -1164,6 +1169,7 @@ class Assembler : public ValueObject {
   // the object pool when possible. Unless you are sure that the untagged object
   // pool pointer is in another register, or that it is not available at all,
   // PP should be passed for pp.
+  void AddImmediate(Register dest, int64_t imm);
   void AddImmediate(Register dest, Register rn, int64_t imm);
   void AddImmediateSetFlags(Register dest, Register rn, int64_t imm);
   void SubImmediateSetFlags(Register dest, Register rn, int64_t imm);