Implement function entry breakpoints in Observatory debugger.

runtime/observatory/lib/src/cli/command.dart

Index: runtime/observatory/lib/src/cli/command.dart
diff --git a/runtime/observatory/lib/src/cli/command.dart b/runtime/observatory/lib/src/cli/command.dart
index ce16a643666f0fe7b540504f19aaf30bda1a7aef..c1da71bc772f50e34ab9ef911ed0c58f87836e33 100644
--- a/runtime/observatory/lib/src/cli/command.dart
+++ b/runtime/observatory/lib/src/cli/command.dart
@@ -190,7 +190,8 @@ abstract class Command extends _CommandBase {
     if (_parent is RootCommand) {
       return name;
     } else {
-      return '${_parent.fullName} $name';
+      Command parent = _parent;
+      return '${parent.fullName} $name';
     }
   }