Fire 'stack' getter of error objects after GC.

src/list-inl.h

Index: src/list-inl.h
diff --git a/src/list-inl.h b/src/list-inl.h
index 60a033df04527ca2678cf46931a8bc86d32163dc..7a84313cd6ad5ed5235b97c5442ef3f520a1cc1a 100644
--- a/src/list-inl.h
+++ b/src/list-inl.h
@@ -85,8 +85,9 @@ void List<T, P>::ResizeAddInternal(const T& element, P alloc) {
 
 template<typename T, class P>
 void List<T, P>::Resize(int new_capacity, P alloc) {
+  ASSERT_LE(length_, new_capacity);
   T* new_data = NewData(new_capacity, alloc);
-  memcpy(new_data, data_, capacity_ * sizeof(T));
+  memcpy(new_data, data_, length_ * sizeof(T));
   List<T, P>::DeleteData(data_);
   data_ = new_data;
   capacity_ = new_capacity;
@@ -162,6 +163,14 @@ void List<T, P>::Rewind(int pos) {
 
 
 template<typename T, class P>
+void List<T, P>::Trim(P alloc) {
+  if (length_ < capacity_ / 4) {
+    Resize(capacity_ / 2, alloc);
+  }
+}
+
+
+template<typename T, class P>
 void List<T, P>::Iterate(void (*callback)(T* x)) {
   for (int i = 0; i < length_; i++) callback(&data_[i]);
 }