Remove service.Class.children, and (mostly) as a side-effect sort the class hierarchy view.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 48f9190b4a4b55f3ba3ee537719d6d347f47529b..5c138fe05b5bbd4ee5c938593c71a2df3bfcc076 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -4175,13 +4175,11 @@ void Class::PrintJSONImpl(JSONStream* stream, bool ref) const {
         GrowableObjectArray::Handle(direct_subclasses());
     if (!subclasses.IsNull()) {
       Class& subclass = Class::Handle();
-      if (!subclasses.IsNull()) {
-        for (intptr_t i = 0; i < subclasses.Length(); ++i) {
-          // TODO(turnidge): Use the Type directly once regis has added
-          // types to the vmservice.
-          subclass ^= subclasses.At(i);
-          subclasses_array.AddValue(subclass);
-        }
+      for (intptr_t i = 0; i < subclasses.Length(); ++i) {
+        // TODO(turnidge): Use the Type directly once regis has added
+        // types to the vmservice.
+        subclass ^= subclasses.At(i);
+        subclasses_array.AddValue(subclass);
       }
     }
   }