Add --check-code-pointer flag for debug builds

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
diff --git a/runtime/vm/assembler_x64.cc b/runtime/vm/assembler_x64.cc
index 85b83a9c9cc99b88b5f677545eaa9a82916a3e5f..02527fc038a39462e3a8bc6dbd7521a2df6fb8b8 100644
--- a/runtime/vm/assembler_x64.cc
+++ b/runtime/vm/assembler_x64.cc
@@ -18,9 +18,11 @@
 namespace dart {
 
 DECLARE_FLAG(bool, allow_absolute_addresses);
-DEFINE_FLAG(bool, print_stop_message, true, "Print stop message.");
+DECLARE_FLAG(bool, check_code_pointer);
 DECLARE_FLAG(bool, inline_alloc);
 
+DEFINE_FLAG(bool, print_stop_message, true, "Print stop message.");
+
 
 Assembler::Assembler(bool use_far_branches)
     : buffer_(),
@@ -3372,6 +3374,9 @@ void Assembler::LeaveDartFrame(RestorePP restore_pp) {
 
 void Assembler::CheckCodePointer() {
 #ifdef DEBUG
+  if (!FLAG_check_code_pointer) {
+    return;
+  }
   Comment("CheckCodePointer");
   Label cid_ok, instructions_ok;
   pushq(RAX);