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

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

Index: runtime/observatory/lib/src/elements/sample_buffer_control.dart
diff --git a/runtime/observatory/lib/src/elements/sample_buffer_control.dart b/runtime/observatory/lib/src/elements/sample_buffer_control.dart
index 3661c7cfd82c28929a51f9f747e43c28f4239cf7..a82734e24f7d647e506ba513c2688d5b585ee244 100644
--- a/runtime/observatory/lib/src/elements/sample_buffer_control.dart
+++ b/runtime/observatory/lib/src/elements/sample_buffer_control.dart
@@ -29,6 +29,7 @@ class SampleBufferControlElement extends HtmlElement implements Renderable {
   Stream<SampleBufferControlChangedElement> get onTagChange =>
       _onTagChange.stream;
 
+  M.VM _vm;
   Stream<M.SampleProfileLoadingProgressEvent> _progressStream;
   M.SampleProfileLoadingProgress _progress;
   M.SampleProfileTag _tag;
@@ -46,17 +47,21 @@ class SampleBufferControlElement extends HtmlElement implements Renderable {
   set showTag(bool value) => _showTag = _r.checkAndReact(_showTag, value);
   set profileVM(bool value) => _profileVM = _r.checkAndReact(_profileVM, value);
 
-  factory SampleBufferControlElement(M.SampleProfileLoadingProgress progress,
+  factory SampleBufferControlElement(
+      M.VM vm,
+      M.SampleProfileLoadingProgress progress,
       Stream<M.SampleProfileLoadingProgressEvent> progressStream,
       {M.SampleProfileTag selectedTag: M.SampleProfileTag.none,
       bool showTag: true,
       RenderingQueue queue}) {
+    assert(vm != null);
     assert(progress != null);
     assert(progressStream != null);
     assert(selectedTag != null);
     assert(showTag != null);
     SampleBufferControlElement e = document.createElement(tag.name);
     e._r = new RenderingScheduler(e, queue: queue);
+    e._vm = vm;
     e._progress = progress;
     e._progressStream = progressStream;
     e._tag = selectedTag;
@@ -129,7 +134,7 @@ class SampleBufferControlElement extends HtmlElement implements Renderable {
     ];
   }
 
-  static List<Element> _createDisabledMessage() {
+  List<Element> _createDisabledMessage() {
     return [
       new DivElement()
         ..classes = ['statusBox' 'shadow' 'center']
@@ -142,8 +147,11 @@ class SampleBufferControlElement extends HtmlElement implements Renderable {
                 ..innerHtml = 'Perhaps the <b>profile</b> '
                     'flag has been disabled for this VM.',
               new BRElement(),
-              new SpanElement()..text = 'See all ',
-              new AnchorElement(href: Uris.flags())..text = 'vm flags'
+              new ButtonElement()
+                ..text = 'Enable profiler'
+                ..onClick.listen((_) {
+                  _enableProfiler();
+                })
             ]
         ]
     ];
@@ -253,5 +261,11 @@ class SampleBufferControlElement extends HtmlElement implements Renderable {
     return new SampleBufferControlChangedElement(this);
   }
 
+  void _enableProfiler() {
+    _vm.enableProfiler().then((_) {
+      _triggerModeChange(_toEvent(null));
+    });
+  }
+
   void _triggerModeChange(e) => _onTagChange.add(e);
 }