Fix SkiaOutputSurfaceImpl crash

There are occasional crashes accessing an empty
|overdraw_surface_recorder_|. Even if |show_overdraw_feedback| is true
creation of the recorded can fail, so using that bool to guard access
isn't correct. Check if the recorded exists before accessing it instead.

Also unconditionally reset |nway_canvas_| since it can be created even
if recorder creation fails.

Bug: 1143631
Change-Id: Ie00eeb11d84eedd589f7d99e62bbb80ab3d16bc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521050
Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824654}

components/viz/service/display_embedder/skia_output_surface_impl.cc

@@ -579,13 +579,13 @@ void SkiaOutputSurfaceImpl::EndPaint(base::OnceClosure on_finished) {
     // Draw on the root render pass.
     current_buffer_modified_ = true;
     sk_sp<SkDeferredDisplayList> overdraw_ddl;
-    if (debug_settings_->show_overdraw_feedback) {
+    if (overdraw_surface_recorder_) {
       overdraw_ddl = overdraw_surface_recorder_->detach();
       DCHECK(overdraw_ddl);
       overdraw_canvas_.reset();
-      nway_canvas_.reset();
       overdraw_surface_recorder_.reset();
     }
+    nway_canvas_.reset();
 
     auto task = base::BindOnce(
         &SkiaOutputSurfaceImplOnGpu::FinishPaintCurrentFrame,