Never use the freelists when always compacting.

src/spaces.cc

Index: src/spaces.cc
===================================================================
--- src/spaces.cc	(revision 2045)
+++ src/spaces.cc	(working copy)
@@ -1332,6 +1332,13 @@
   FreeListNode* node = FreeListNode::FromAddress(start);
   node->set_size(size_in_bytes);
 
+  // We don't use the freelists in compacting mode.  This makes it more like a
+  // GC that only has mark-sweep-compact and doesn't have a mark-sweep
+  // collector.
+  if (FLAG_always_compact) {
+    return size_in_bytes;
+  }
+
   // Early return to drop too-small blocks on the floor (one or two word
   // blocks cannot hold a map pointer, a size field, and a pointer to the
   // next block in the free list).