Debug garbage collector does not correctly remove cross-gen garbage

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index 4998b881cfdc1c4876e1cbf79b991a4853aaa9c1..bc3a057e5b47f93aae419b9709c1b4e9e02e12cd 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -38,7 +38,8 @@ Heap::Heap(Isolate* isolate,
       barrier_done_(new Monitor()),
       read_only_(false),
       gc_new_space_in_progress_(false),
-      gc_old_space_in_progress_(false) {
+      gc_old_space_in_progress_(false),
+      debug_gc_in_progress_(false) {
   UpdateGlobalMaxUsed();
   for (int sel = 0; sel < kNumWeakSelectors; sel++) {
     new_weak_tables_[sel] = new WeakTable();
@@ -444,8 +445,10 @@ void Heap::CollectGarbage(Space space) {
 
 void Heap::CollectAllGarbage() {
   Thread* thread = Thread::Current();
-  CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
+  debug_gc_in_progress_ = true;
   CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
+  CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
+  debug_gc_in_progress_ = false;
 }