Bug 1421651 - Remove obseleted timeline and TimelineMarker code r=canaltinova,webidl,devtools-reviewers,saschanaz,smaug,ochameau

This patch removes the old docshell timeline and timeline markers codebase and replaces them with equivalent Gecko profiler marker. This patch also fixes Bug 1834143, which is a subset of 1421651.

Differential Revision: https://phabricator.services.mozilla.com/D184217

layout/base/nsDocumentViewer.cpp

@@ -96,8 +96,6 @@
 #include "nsIXULRuntime.h"
 #include "nsSandboxFlags.h"
 
-#include "mozilla/DocLoadingTimelineMarker.h"
-
 //--------------------------
 // Printing Include
 //---------------------------
@@ -1023,12 +1021,6 @@ nsDocumentViewer::LoadComplete(nsresult aStatus) {
                             nullptr);
       }
 
-      // Notify any devtools about the load.
-      if (TimelineConsumers::HasConsumer(docShell)) {
-        TimelineConsumers::AddMarkerForDocShell(
-            docShell, MakeUnique<DocLoadingTimelineMarker>("document::Load"));
-      }
-
       nsPIDOMWindowInner* innerWindow = window->GetCurrentInnerWindow();
       RefPtr<DocGroup> docGroup = d->GetDocGroup();
       // It is possible that the parent document's load event fires earlier than