[vm] Don't enable the profiler by default. Enable the profiler at startup with --observe, or later …

runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart

Index: runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
diff --git a/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart b/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
index 77e1a724f7f84056aa895f76af2c7c440a108f52..daa65793dd4ab1b04ed50181469d456889636799 100644
--- a/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
+++ b/runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.dart
@@ -128,6 +128,14 @@ class CpuProfileVirtualTreeElement extends HtmlElement implements Renderable {
     }
     _tree = new VirtualTreeElement(create, update, _getChildren,
         items: tree.root.children, queue: _r.queue);
+    if (tree.root.children.length == 0) {
+      children = [
+        new DivElement()
+          ..classes = ['tree-item']
+          ..children = [new HeadingElement.h1()..text = 'No Samples']
+      ];
+      return;
+    }
     if (tree.root.children.length == 1) {

[cbernaschina, 2017/07/31 21:19:13]

Consider switch or else if

[rmacnak, 2017/08/01 19:58:58]

Done.

       _tree.expand(tree.root.children.first, autoExpandSingleChildNodes: true);
     }