Rendering text to a canvas in a frame-less document.

third_party/WebKit/Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2869 matching lines @@
     if (!hasRareData() && size == defaultMinimumSizeForResizing())
         return;
     ensureElementRareData().setMinimumSizeForResizing(size);
 }
 
 const ComputedStyle* Element::ensureComputedStyle(PseudoId pseudoElementSpecifier)
 {
     if (PseudoElement* element = pseudoElement(pseudoElementSpecifier))
         return element->ensureComputedStyle();
 
-    if (!inActiveDocument()) {
+    if (!inActiveDocument() && document().frame()) {

[esprehn, 2016/09/26 22:23:37]

This is not correct, it means we don't return null here if your document had no
frame. Which makes us call ensureStyleResolver below on an frameless document
which will crash.

inActiveDocument() is guarding the code below. I'm also curious why you'd want
to run the style code for elements not in the document but inside a frameless
document? It seems strange we'd special case on frame here, in general this code
shouldn't care about that, it's about being in an active document (capable of
computing style) or not.

         // FIXME: Try to do better than this. Ensure that styleForElement() works for elements that are not in the
         // document tree and figure out when to destroy the computed style for such elements.
         return nullptr;
     }
 
     // FIXME: Find and use the layoutObject from the pseudo element instead of the actual element so that the 'length'
     // properties, which are only known by the layoutObject because it did the layout, will be correct and so that the
     // values returned for the ":selection" pseudo-element will be correct.
     ComputedStyle* elementStyle = mutableComputedStyle();
     if (!elementStyle) {
@@ skipping 925 matching lines @@
 
 DEFINE_TRACE_WRAPPERS(Element)
 {
     if (hasRareData()) {
         visitor->traceWrappers(elementRareData());
     }
     ContainerNode::traceWrappers(visitor);
 }
 
 } // namespace blink