Bug 1780455 - Fix an assertion to account for imagemap hacks. r=jwatt

I tried to add a crashtest without the video attachment and so on but
that didn't quite make it.

Differential Revision: https://phabricator.services.mozilla.com/D152374

layout/base/PresShell.cpp

@@ -3015,7 +3015,8 @@ static void AssertNoFramesOrStyleDataInDescendants(Element& aElement) {
     if (c == &aElement) {
       continue;
     }
-    MOZ_ASSERT(!c->GetPrimaryFrame());
+    // FIXME(emilio): The <area> check is needed because of bug 135040.
+    MOZ_ASSERT(!c->GetPrimaryFrame() || c->IsHTMLElement(nsGkAtoms::area));
     MOZ_ASSERT(!c->IsElement() || !c->AsElement()->HasServoData());
   }
 }