[vm] Get a reference backtrace if we encounter disabled code when writing an AOT snapshot.

runtime/vm/clustered_snapshot.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/clustered_snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 1581 matching lines @@
     intptr_t count = objects_.length();
     for (intptr_t i = 0; i < count; i++) {
       RawCode* code = objects_[i];
 
       intptr_t pointer_offsets_length =
           Code::PtrOffBits::decode(code->ptr()->state_bits_);
       if (pointer_offsets_length != 0) {
         FATAL("Cannot serialize code with embedded pointers");
       }
       if (kind == Snapshot::kFullAOT) {
-        // No disabled code in precompilation.
-        NOT_IN_PRECOMPILED(ASSERT(code->ptr()->instructions_ ==
-                                  code->ptr()->active_instructions_));
+        if (code->ptr()->instructions_ != code->ptr()->active_instructions_) {
+          s->UnexpectedObject(code, "Disabled code");
+        }
       }
 
       RawInstructions* instr = code->ptr()->instructions_;
       int32_t text_offset = s->GetTextOffset(instr, code);
       s->Write<int32_t>(text_offset);
       if (s->kind() == Snapshot::kFullJIT) {
         // TODO(rmacnak): Fix references to disabled code before serializing.
         if (code->ptr()->active_instructions_ != code->ptr()->instructions_) {
           instr = code->ptr()->active_instructions_;
           text_offset = s->GetTextOffset(instr, code);
@@ skipping 4027 matching lines @@
     thread_->isolate()->SetupImagePage(data_buffer_,
                                        /* is_executable */ false);
   }
 
   deserializer.ReadIsolateSnapshot(thread_->isolate()->object_store());
 
   return ApiError::null();
 }
 
 }  // namespace dart