Ignore same document navigations when updating subframe navigation start.

Bug: 1104365
Change-Id: I20491cecfaf80abe4194f24005938c623911c7f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298179
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788720}

chrome/browser/page_load_metrics/observers/amp_page_load_metrics_observer.cc

@@ -130,6 +130,10 @@ void AMPPageLoadMetricsObserver::OnDidFinishSubFrameNavigation(
   if (!navigation_handle->HasCommitted())
     return;
 
+  // Ignore same document navigations; see crbug.com/1104365
+  if (navigation_handle->IsSameDocument())
+    return;
+
   // A new navigation is committing, so ensure any old information associated
   // with this frame is discarded.
   amp_subframe_info_.erase(navigation_handle->GetRenderFrameHost());