Don't visit a frame's code object twice.

runtime/vm/stack_frame.cc

 // Copyright (c) 2012, 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/stack_frame.h"
 
 #include "platform/memory_sanitizer.h"
 #include "vm/assembler.h"
 #include "vm/deopt_instructions.h"
 #include "vm/isolate.h"
@@ skipping 79 matching lines @@
   // NOTE: This code runs while GC is in progress and runs within
   // a NoHandleScope block. Hence it is not ok to use regular Zone or
   // Scope handles. We use direct stack handles, the raw pointers in
   // these handles are not traversed. The use of handles is mainly to
   // be able to reuse the handle based code and avoid having to add
   // helper functions to the raw object interface.
   NoSafepointScope no_safepoint;
   Code code;
   code = GetCodeObject();
   if (!code.IsNull()) {
-    // Visit the code object.
-    RawObject* raw_code = code.raw();
-    visitor->VisitPointer(&raw_code);
-
     // Optimized frames have a stack map. We need to visit the frame based
     // on the stack map.
     Array maps;
     maps = Array::null();
     StackMap map;
     const uword start = Instructions::PayloadStart(code.instructions());
     map = code.GetStackMap(pc() - start, &maps, &map);
     if (!map.IsNull()) {
 #if !defined(TARGET_ARCH_DBC)
       RawObject** first = reinterpret_cast<RawObject**>(sp());
@@ skipping 469 matching lines @@
   StackFrameIterator frames(StackFrameIterator::kValidateFrames);
   StackFrame* frame = frames.NextFrame();
   while (frame != NULL) {
     frame = frames.NextFrame();
   }
 }
 #endif
 
 
 }  // namespace dart