Bump allocation for promotion

runtime/vm/freelist.h

Index: runtime/vm/freelist.h
===================================================================
--- runtime/vm/freelist.h	(revision 39806)
+++ runtime/vm/freelist.h	(working copy)
@@ -94,7 +94,14 @@
 
   // Returns a large element, at least 'minimum_size', or NULL if none exists.
   FreeListElement* TryAllocateLarge(intptr_t minimum_size);
+  FreeListElement* TryAllocateLargeLocked(intptr_t minimum_size);
 
+  // Allocates locked and unprotected memory, but only from small elements
+  // (i.e., fixed size lists).
+  uword TryAllocateSmall(intptr_t size);
+  // Returns 'b' such that all small elements have size <= 'b' bytes.
+  intptr_t SmallSizeBound() const { return last_free_small_size_; }
+
  private:
   static const int kNumLists = 128;
 
@@ -119,6 +126,9 @@
 
   FreeListElement* free_lists_[kNumLists + 1];
 
+  // The largest available small size in bytes, or negative if there is none.
+  intptr_t last_free_small_size_;
+
   DISALLOW_COPY_AND_ASSIGN(FreeList);
 };