Call blink::mojom::LocalFrameHost::DocumentOnLoadCompleted() earlier

Today, this mojo call comes from LocalFrameClientImpl::DispatchDidHandleOnloadEvents(),
which used to make sense when RenderFrameImpl::DispatchDidHandleOnloadEvents()
used to send the respective message to content::mojom::FrameHost interface,
and calling observers.

Now that this mojo message got moved from content.mojom.FrameHost to
blink.mojom.LocalFrameHost [1], it seems logical to call it from out
of LocalFrameClientImpl class.

BUG=1043760
R=dtapuska@chromium.org

Change-Id: Ie3917cca5fa687a3d7ede91970321c6d1aa8f3a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2014763Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Auto-Submit: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#734053}

third_party/blink/renderer/core/dom/document.cc

@@ -3636,6 +3636,9 @@ void Document::ImplicitClose() {
   if (domWindow())
     domWindow()->DocumentWasClosed();
 
+  if (GetFrame() && GetFrame()->IsMainFrame())
+    GetFrame()->GetLocalFrameHostRemote().DocumentOnLoadCompleted();
+
   if (GetFrame()) {
     GetFrame()->Client()->DispatchDidHandleOnloadEvents();
     Loader()->GetApplicationCacheHost()->StopDeferringEvents();

third_party/blink/renderer/core/exported/local_frame_client_impl.cc

@@ -387,8 +387,6 @@ void LocalFrameClientImpl::DispatchDidLoadResourceFromMemoryCache(
 }
 
 void LocalFrameClientImpl::DispatchDidHandleOnloadEvents() {
-  if (!web_frame_->Parent())
-    web_frame_->GetFrame()->GetLocalFrameHostRemote().DocumentOnLoadCompleted();
   if (web_frame_->Client())
     web_frame_->Client()->DidHandleOnloadEvents();
 }