[Blink/SPv175] Early out GraphicsLayer::Paint when layer state is invalid

This is a band-aid for a null pointer crash when layer_state_ is accessed.
We don't know why a null state can ever happen, and there is no meaningful
fallback. This CL skips painting for the offending layer so at least it
won't crash.

BUG=853096

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I52ae41253440d6937909cc69f1711852fc4efd6b
Reviewed-on: https://chromium-review.googlesource.com/1105342Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Tien-Ren Chen <trchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568276}

third_party/blink/renderer/platform/graphics/graphics_layer.cc

@@ -337,6 +337,13 @@ void GraphicsLayer::PaintRecursivelyInternal(
 
 bool GraphicsLayer::Paint(const IntRect* interest_rect,
                           GraphicsContext::DisabledMode disabled_mode) {
+#if !DCHECK_IS_ON()
+  // TODO(crbug.com/853096): Investigate why we can ever reach here without
+  // a valid layer state. Seems to only happen on Android builds.
+  if (RuntimeEnabledFeatures::SlimmingPaintV175Enabled() && !layer_state_)
+    return false;
+#endif
+
   if (PaintWithoutCommit(interest_rect, disabled_mode))
     GetPaintController().CommitNewDisplayItems();
   else if (!needs_check_raster_invalidation_)