Restrict floating control to minimal control-connected component.

src/zone-allocator.h

Index: src/zone-allocator.h
diff --git a/src/zone-allocator.h b/src/zone-allocator.h
index ab0ae9cf606ddb446b3b79756baa69a72221ae6d..1eb69b89dd70642cf7eba8210f2903b53f3f6c6a 100644
--- a/src/zone-allocator.h
+++ b/src/zone-allocator.h
@@ -50,10 +50,10 @@ class zone_allocator {
   }
   void destroy(pointer p) { p->~T(); }
 
-  bool operator==(zone_allocator const& other) {
+  bool operator==(zone_allocator const& other) const {
     return zone_ == other.zone_;
   }
-  bool operator!=(zone_allocator const& other) {
+  bool operator!=(zone_allocator const& other) const {
     return zone_ != other.zone_;
   }