Handle SVGLength resolving in an inactive document gracefully

Source/core/svg/SVGLengthContext.cpp

Index: Source/core/svg/SVGLengthContext.cpp
diff --git a/Source/core/svg/SVGLengthContext.cpp b/Source/core/svg/SVGLengthContext.cpp
index 64a81dc98699c57e63e50401072efcbf735cdd86..50e381f3e9e6e7ec4a973cc2749a37a8e21af1d0 100644
--- a/Source/core/svg/SVGLengthContext.cpp
+++ b/Source/core/svg/SVGLengthContext.cpp
@@ -65,8 +65,8 @@ static const ComputedStyle* computedStyleForLengthResolving(const SVGElement* co
         currentContext = currentContext->parentNode();
     } while (currentContext);
 
-    // There must be at least a LayoutSVGRoot layoutObject, carrying a style.
-    ASSERT_NOT_REACHED();
+    // We can end up here if trying to resolve values for elements in an
+    // inactive document.
     return nullptr;
 }