Object pool with support for untagged entries.

runtime/vm/assembler_x64.h

Index: runtime/vm/assembler_x64.h
diff --git a/runtime/vm/assembler_x64.h b/runtime/vm/assembler_x64.h
index 4bf6a573efca76738d757ab6683f71ae155d6910..5cdb0cf74d049d9d4a8d3cb3e167397e1229f809 100644
--- a/runtime/vm/assembler_x64.h
+++ b/runtime/vm/assembler_x64.h
@@ -902,11 +902,10 @@ class Assembler : public ValueObject {
   const ZoneGrowableArray<intptr_t>& GetPointerOffsets() const {
     return buffer_.pointer_offsets();
   }
-  const GrowableObjectArray& object_pool_data() const {
-    return object_pool_.data();
-  }
 
-  ObjectPool& object_pool() { return object_pool_; }
+  ObjectPoolHelper& object_pool() { return object_pool_; }
+
+  RawObjectPool* MakeObjectPool() { return object_pool_.MakeObjectPool(); }
 
   void FinalizeInstructions(const MemoryRegion& region) {
     buffer_.FinalizeInstructions(region);
@@ -1033,8 +1032,7 @@ class Assembler : public ValueObject {
  private:
   AssemblerBuffer buffer_;
 
-  // Objects and jump targets.
-  ObjectPool object_pool_;
+  ObjectPoolHelper object_pool_;
 
   intptr_t prologue_offset_;