Enable iterating over roots from helper threads by moving stack walking.

runtime/vm/thread_registry.h

Index: runtime/vm/thread_registry.h
diff --git a/runtime/vm/thread_registry.h b/runtime/vm/thread_registry.h
index f8f324dc752a2215edfa592086b3d5fbcd1944d3..b7d3e1a8a0877f2e1217c8c0925b77dc46be71be 100644
--- a/runtime/vm/thread_registry.h
+++ b/runtime/vm/thread_registry.h
@@ -9,6 +9,7 @@
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
+#include "vm/stack_frame.h"
 #include "vm/thread.h"
 
 namespace dart {
@@ -118,9 +119,19 @@ class ThreadRegistry {
     MonitorLocker ml(monitor_);
     for (int i = 0; i < entries_.length(); ++i) {
       const Entry& entry = entries_[i];
-      Zone* zone = entry.scheduled ? entry.thread->zone() : entry.state.zone;
-      if (zone != NULL) {
-        zone->VisitObjectPointers(visitor);
+      const Thread::State& state =
+          entry.scheduled ? entry.thread->state_ : entry.state;
+      if (state.zone != NULL) {
+        state.zone->VisitObjectPointers(visitor);
+      }
+      // Iterate over all the stack frames and visit objects on the stack.
+      uword efi = state.top_exit_frame_info;
+      if (efi == 0) continue;
+      StackFrameIterator frames_iterator(efi, false);

[Ivan Posva, 2015/08/11 17:41:31]

Please do not use explicit constants and use the appropriately named constant
StackFrameIterator::kDontValidateFrames.

+      StackFrame* frame = frames_iterator.NextFrame();
+      while (frame != NULL) {
+        frame->VisitObjectPointers(visitor);
+        frame = frames_iterator.NextFrame();
       }
     }
   }