Investigate & fix issues around usage_count and deoptimization_count

runtime/vm/weak_code.cc

Index: runtime/vm/weak_code.cc
diff --git a/runtime/vm/weak_code.cc b/runtime/vm/weak_code.cc
index e6422046c81d6575a967e6281809ba03a7389e14..7c817d03ab8843fdd9c34869e75e3b5c926fb9b6 100644
--- a/runtime/vm/weak_code.cc
+++ b/runtime/vm/weak_code.cc
@@ -14,6 +14,11 @@
 
 namespace dart {
 
+bool WeakCodeReferences::HasCodes() const {
+  return !array_.IsNull() && (array_.Length() > 0);
+}
+
+
 void WeakCodeReferences::Register(const Code& value) {
   if (!array_.IsNull()) {
     // Try to find and reuse cleared WeakProperty to avoid allocating new one.