Use off-heap data for class check instructions

runtime/vm/assembler_arm64.cc

Index: runtime/vm/assembler_arm64.cc
diff --git a/runtime/vm/assembler_arm64.cc b/runtime/vm/assembler_arm64.cc
index af6c89159241cc89f54417ad7da380a1607ddfaa..4fc5058332a244f328ca0f7bf3dea56c4355920f 100644
--- a/runtime/vm/assembler_arm64.cc
+++ b/runtime/vm/assembler_arm64.cc
@@ -620,6 +620,11 @@ void Assembler::BranchLinkWithEquivalence(const StubEntry& stub_entry,
 }
 
 
+void Assembler::AddImmediate(Register dest, int64_t imm) {
+  AddImmediate(dest, dest, imm);
+}
+
+
 void Assembler::AddImmediate(Register dest, Register rn, int64_t imm) {
   Operand op;
   if (imm == 0) {