Initial UserTag and dart:profiler library

runtime/vm/object_store.cc

Index: runtime/vm/object_store.cc
diff --git a/runtime/vm/object_store.cc b/runtime/vm/object_store.cc
index bc9e3262480155db249fa1d7d9029a233be997de..ce9cb16b0898cf781cffdb136e8ab2d3d67438e3 100644
--- a/runtime/vm/object_store.cc
+++ b/runtime/vm/object_store.cc
@@ -53,6 +53,9 @@ ObjectStore::ObjectStore()
     jsregexp_class_(Class::null()),
     weak_property_class_(Class::null()),
     mirror_reference_class_(Class::null()),
+    user_tag_class_(Class::null()),
+    tag_table_(GrowableObjectArray::null()),
+    current_tag_(UserTag::null()),
     symbol_table_(Array::null()),
     canonical_type_arguments_(Array::null()),
     async_library_(Library::null()),
@@ -123,6 +126,9 @@ bool ObjectStore::PreallocateObjects() {
   }
   set_stack_overflow(Instance::Cast(result));
 
+  ASSERT(this->tag_table() == GrowableObjectArray::null());
+  this->tag_table_ = GrowableObjectArray::New();
+
   result = DartLibraryCalls::InstanceCreate(library,
                                             Symbols::OutOfMemoryError(),
                                             Symbols::Dot(),