Fire 'stack' getter of error objects after GC.

src/list.h

Index: src/list.h
diff --git a/src/list.h b/src/list.h
index 7fd4f5cd2d6f6af7b8e2675252347b560c95dbdd..43d982f687a7b37bfe55a128f47e9e8ee8c12eea 100644
--- a/src/list.h
+++ b/src/list.h
@@ -149,6 +149,9 @@ class List {
   // Drop the last 'count' elements from the list.
   INLINE(void RewindBy(int count)) { Rewind(length_ - count); }
 
+  // Halve the capacity if fill level is less than a quarter.
+  INLINE(void Trim(AllocationPolicy allocator = AllocationPolicy()));
+
   bool Contains(const T& elm) const;
   int CountOccurrences(const T& elm, int start, int end) const;