Check RF is alive In PrintRenderFrameHelper::PreviewPageRendered().

Do not take an accessibility snapshot if the RenderFrame is gone.

Bug: 1133983
Change-Id: I612cc72936a1dcedc5180c24eae067e47237b09b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2442375Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812851}

components/printing/renderer/print_render_frame_helper.cc

@@ -2467,6 +2467,10 @@ bool PrintRenderFrameHelper::PreviewPageRendered(
                "page_number", page_number);
 
 #if BUILDFLAG(ENABLE_TAGGED_PDF)
+  // Make sure the RenderFrame is alive before taking the snapshot.
+  if (render_frame_gone_)
+    snapshotter_.reset();
+
   // For tagged PDF exporting, send a snapshot of the accessibility tree
   // along with page 0. The accessibility tree contains the content for
   // all of the pages of the main frame.