Support untagged object pool entries.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 217f30f4bf54851e7e75a45ce60e0de3add2c71d..d43424ef5d2e9cec7446ef1a4d2c9cb69bf7d763 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -31,6 +31,7 @@ namespace dart {
   V(Namespace)                                                                 \
   V(Code)                                                                      \
   V(Instructions)                                                              \
+  V(ObjectPool)                                                                \
   V(PcDescriptors)                                                             \
   V(Stackmap)                                                                  \
   V(LocalVarDescriptors)                                                       \
@@ -991,6 +992,28 @@ class RawCode : public RawObject {
 };
 
 
+class RawObjectPool : public RawObject {
+  RAW_HEAP_OBJECT_IMPLEMENTATION(ObjectPool);
+
+  intptr_t length_;
+  intptr_t num_tagged_entries_;
+
+  struct Entry {
+    union {
+      RawObject* raw_obj_;
+      uword raw_value_;
+    };
+  };
+  Entry* data() { OPEN_ARRAY_START(Entry, Entry); }
+  Entry const* data() const { OPEN_ARRAY_START(Entry, Entry); }
+
+  Entry* from();
+  Entry* to();
+
+  friend class Object;
+};
+
+
 class RawInstructions : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Instructions);
 
@@ -998,7 +1021,7 @@ class RawInstructions : public RawObject {
     return reinterpret_cast<RawObject**>(&ptr()->code_);
   }
   RawCode* code_;
-  RawArray* object_pool_;
+  RawObjectPool* object_pool_;
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->object_pool_);
   }
@@ -2098,6 +2121,7 @@ inline bool RawObject::IsVariableSizeClassId(intptr_t index) {
          (index == kContextCid) ||
          (index == kTypeArgumentsCid) ||
          (index == kInstructionsCid) ||
+         (index == kObjectPoolCid) ||
          (index == kPcDescriptorsCid) ||
          (index == kStackmapCid) ||
          (index == kLocalVarDescriptorsCid) ||