Expose a lower bound of malloc'd memory via heap statistics

src/zone.h

Index: src/zone.h
diff --git a/src/zone.h b/src/zone.h
index 753e2035d3ac612060cb1391c33f29db5df9110f..fa21155fe10da907cda627a836a804ff10a272a9 100644
--- a/src/zone.h
+++ b/src/zone.h
@@ -7,7 +7,7 @@
 
 #include <limits>
 
-#include "src/allocation.h"
+#include "src/base/accounting-allocator.h"
 #include "src/base/logging.h"
 #include "src/globals.h"
 #include "src/hashmap.h"
@@ -35,7 +35,7 @@ class Segment;
 // from multi-threaded code.
 class Zone final {
  public:
-  Zone();
+  explicit Zone(base::AccountingAllocator* allocator);
   ~Zone();
 
   // Allocate 'size' bytes of memory in the Zone; expands the Zone by
@@ -64,6 +64,8 @@ class Zone final {
 
   size_t allocation_size() const { return allocation_size_; }
 
+  base::AccountingAllocator* allocator() const { return allocator_; }
+
  private:
   // All pointers returned from New() have this alignment.  In addition, if the
   // object being allocated has a size that is divisible by 8 then its alignment
@@ -114,6 +116,8 @@ class Zone final {
   Address position_;
   Address limit_;
 
+  base::AccountingAllocator* allocator_;
+
   Segment* segment_head_;
 };