Fix crash in AccessibilityMediaElement

R=aboxhall@chromium.org

Bug: 1167269
Change-Id: I5bb0f5fac139dcf16631482e4a21a85e41bd92c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2636892
Auto-Submit: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845141}

third_party/blink/renderer/modules/accessibility/ax_media_element.cc

@@ -58,15 +58,21 @@ AXRestriction AccessibilityMediaElement::Restriction() const {
 }
 
 bool AccessibilityMediaElement::HasControls() const {
+  if (IsDetached())
+    return false;
   return To<HTMLMediaElement>(GetNode())->ShouldShowControls();
 }
 
 bool AccessibilityMediaElement::HasEmptySource() const {
+  if (IsDetached())
+    return false;
   return To<HTMLMediaElement>(GetNode())->getNetworkState() ==
          HTMLMediaElement::kNetworkEmpty;
 }
 
 bool AccessibilityMediaElement::IsUnplayable() const {
+  if (IsDetached())
+    return true;
   HTMLMediaElement* element =
       static_cast<HTMLMediaElement*>(layout_object_->GetNode());
   HTMLMediaElement::NetworkState network_state = element->getNetworkState();