Add ability for embedder to provide private timeline trace data

runtime/vm/timeline.cc

Index: runtime/vm/timeline.cc
diff --git a/runtime/vm/timeline.cc b/runtime/vm/timeline.cc
index 2fa59ef6b9f4ead3a48cf1dd0fb58d3220988d24..4072d80689482c2ed031ae7066ad0b80edd1c79e 100644
--- a/runtime/vm/timeline.cc
+++ b/runtime/vm/timeline.cc
@@ -155,6 +155,22 @@ void Timeline::SetVMStreamEnabled(bool enabled) {
 }
 
 
+void Timeline::StreamStateChange(const char* stream_name,
+                                 bool prev,
+                                 bool curr) {
+  if (prev == curr) {
+    return;
+  }
+  if (strcmp(stream_name, "Embedder") == 0) {
+    if (curr && (Timeline::get_start_recording_cb() != NULL)) {
+      Timeline::get_start_recording_cb()();
+    } else if (!curr && (Timeline::get_stop_recording_cb() != NULL)) {
+      Timeline::get_stop_recording_cb()();
+    }
+  }
+}
+
+
 void Timeline::Shutdown() {
   ASSERT(recorder_ != NULL);
   if (FLAG_timeline_dir != NULL) {
@@ -273,6 +289,9 @@ TimelineEventRecorder* Timeline::recorder_ = NULL;
 TimelineStream Timeline::vm_stream_;
 TimelineStream Timeline::vm_api_stream_;
 MallocGrowableArray<char*>* Timeline::enabled_streams_ = NULL;
+Dart_EmbedderTimelineStartRecording Timeline::start_recording_cb_ = NULL;
+Dart_EmbedderTimelineStopRecording Timeline::stop_recording_cb_ = NULL;
+Dart_EmbedderTimelineGetTimeline Timeline::get_timeline_cb_ = NULL;
 
 #define ISOLATE_TIMELINE_STREAM_DEFINE_FLAG(name, enabled_by_default)          \
   bool Timeline::stream_##name##_enabled_ = enabled_by_default;