Make sure heap is iteratable before iterating it.

This line was accidentally removed in r9489.

TBR=kmillikin@chromium.org

BUG=
TEST=

Review URL: http://codereview.chromium.org//8086018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9497 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/debug.cc

@@ -1778,6 +1778,10 @@ void Debug::PrepareForBreakPoints() {
     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;