Add a helper function for allocation of deoptimization history.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 23242)
+++ runtime/vm/object.cc	(working copy)
@@ -53,6 +53,7 @@
 DECLARE_FLAG(bool, trace_compiler);
 DECLARE_FLAG(bool, eliminate_type_checks);
 DECLARE_FLAG(bool, enable_type_checks);
+DECLARE_FLAG(int, deoptimization_counter_threshold);
 
 static const char* kGetterPrefix = "get:";
 static const intptr_t kGetterPrefixLength = strlen(kGetterPrefix);
@@ -3418,6 +3419,15 @@
 }
 
 
+void Function::EnsureDeoptHistory() const {
+  Array& array = Array::Handle(deopt_history());
+  if (array.IsNull()) {
+    array = Array::New(FLAG_deoptimization_counter_threshold);
+    set_deopt_history(array);
+  }
+}
+
+
 RawContextScope* Function::context_scope() const {
   if (IsClosureFunction()) {
     const Object& obj = Object::Handle(raw_ptr()->data_);