Remove GetIsolationInfo() call in third_party_metrics_observer DCHECK.

NavigationHandle::GetIsolationInfo() calls into RenderFrameTreeNode and
RenderFrameImpl to calculate the IsolationInfo for navigation. This in
turn calls into other RenderFrameTreeNodes.

ThirdPartyMetricsObserver::OnDidFinishSubFrameNavigation(), which is
where the DCHECK is, can be called in the destructor of a
RenderFrameImpl and RenderFrameTreeNode, so this re-entrancy while in
the middle of a destructor. Worse, we could already have deleted the
other RenderFrameTreeNodes at this point, resulting in dereferencing
a destroyed object.

Fixed: 1070142
Change-Id: I1d2122ce867160cabfbad6499177c276fd66956a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2146933Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758511}

chrome/browser/page_load_metrics/observers/third_party_metrics_observer.cc

@@ -160,8 +160,6 @@ void ThirdPartyMetricsObserver::OnDidFinishSubFrameNavigation(
     content::NavigationHandle* navigation_handle) {
   largest_contentful_paint_handler_.OnDidFinishSubFrameNavigation(
       navigation_handle, GetDelegate());
-  DCHECK(navigation_handle->GetIsolationInfo().top_frame_origin());
-
   if (!navigation_handle->HasCommitted())
     return;