Make sure heap is iteratable before iterating it.

src/debug.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1760 matching lines @@
     Deoptimizer::DeoptimizeAll();
 
     Handle<Code> lazy_compile =
         Handle<Code>(isolate_->builtins()->builtin(Builtins::kLazyCompile));
 
     // Keep the list of activated functions in a handlified list as it
     // is used both in GC and non-GC code.
     List<Handle<JSFunction> > active_functions(100);
 
     {
+      // We are going to iterate heap to find all functions without
+      // debug break slots.
+      isolate_->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask);
+
       // Ensure no GC in this scope as we are comparing raw pointer
       // values and performing a heap iteration.
       AssertNoAllocation no_allocation;
 
       // Find all non-optimized code functions with activation frames on
       // the stack.
       for (JavaScriptFrameIterator it(isolate_); !it.done(); it.Advance()) {
         JavaScriptFrame* frame = it.frame();
         if (frame->function()->IsJSFunction()) {
           JSFunction* function = JSFunction::cast(frame->function());
@@ skipping 1592 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal