[observatory] Default sort allocation profiles by size instead of name.

runtime/observatory/lib/src/elements/allocation_profile.dart

Index: runtime/observatory/lib/src/elements/allocation_profile.dart
diff --git a/runtime/observatory/lib/src/elements/allocation_profile.dart b/runtime/observatory/lib/src/elements/allocation_profile.dart
index 50de87e286ba59ed5be802cfef7819a4a08ec414..441091dc151cd468dad39acd83b84d3d7b3a39df 100644
--- a/runtime/observatory/lib/src/elements/allocation_profile.dart
+++ b/runtime/observatory/lib/src/elements/allocation_profile.dart
@@ -64,8 +64,8 @@ class AllocationProfileElement extends HtmlElement implements Renderable {
   bool _autoRefresh = false;
   bool _isCompacted = false;
   StreamSubscription _gcSubscription;
-  _SortingField _sortingField = _SortingField.className;
-  _SortingDirection _sortingDirection = _SortingDirection.ascending;
+  _SortingField _sortingField = _SortingField.currentSize;
+  _SortingDirection _sortingDirection = _SortingDirection.descending;
 
   M.VMRef get vm => _vm;
   M.IsolateRef get isolate => _isolate;