Timeline: fix exception when updating tree view details and Events tree experiment is off

third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js

Index: third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
index 63529f44c6e61e41fed52b44b6669ef31b9ca78f..9731c0c08bcff828ffe3148c5a677d190cd52e09 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
@@ -185,6 +185,9 @@ WebInspector.TimelineTreeView.prototype = {
 
     _updateDetailsForSelection: function()
     {
+        // FIXME: remove this as we implement details for all modes.
+        if (!this._detailsView)
+            return;
         var selectedNode = this._dataGrid.selectedNode ? /** @type {!WebInspector.TimelineTreeView.GridNode} */ (this._dataGrid.selectedNode)._profileNode : null;
         if (selectedNode === this._lastSelectedNode)
             return;