Ignore title="" for <style> and <link> in shadow trees

Fixes WICG/webcomponents#535.

source

@@ -12771,8 +12771,9 @@ interface <dfn>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
 
   <p>The <dfn><code data-x="attr-link-title">title</code></dfn> attribute gives the title of the
   link. With one exception, it is purely advisory. The value is text. The exception is for style
-  sheet links, where the <code data-x="attr-link-title">title</code> attribute defines
-  <span data-x="CSS style sheet set">CSS style sheet sets</span>.</p>
+  sheet links that are <span>in a document tree</span>, for which the <code
+  data-x="attr-link-title">title</code> attribute defines <span data-x="CSS style sheet set">CSS
+  style sheet sets</span>.</p>
 
   <p class="note">The <code data-x="attr-link-title">title</code> attribute on <code>link</code>
   elements differs from the global <code data-x="attr-title">title</code> attribute of most other
@@ -14148,7 +14149,9 @@ interface <dfn>HTMLStyleElement</dfn> : <span>HTMLElement</span> {
   <code>style</code> elements defines <span data-x="CSS style sheet set">CSS style sheet
   sets</span>. If the <code>style</code> element has no <code data-x="attr-style-title">title</code>
   attribute, then it has no title; the <code data-x="attr-title">title</code> attribute of ancestors
-  does not apply to the <code>style</code> element. <ref spec=CSSOM></p>
+  does not apply to the <code>style</code> element. If the <code>style</code> element is not
+  <span>in a document tree</span>, then the <code data-x="attr-style-title">title</code> attribute
+  is ignored. <ref spec=CSSOM></p>
 
   <p class="note">The <code data-x="attr-style-title">title</code> attribute on <code>style</code>
   elements, like the <code data-x="attr-link-title">title</code> attribute on <code>link</code>
@@ -14251,7 +14254,8 @@ c-end         = "-->"</pre>
 
      <dd>
 
-      <p>The <code data-x="attr-style-title">title</code> attribute of <var>element</var>.</p>
+      <p>The <code data-x="attr-style-title">title</code> attribute of <var>element</var>, if
+      <var>element</var> is <span>in a document tree</span>, or the empty string otherwise.</p>
 
       <p class="note">Again, this is a <em>reference</em> to the attribute.</p>
 
@@ -23408,7 +23412,8 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
 
      <dd>
 
-      <p>The <code data-x="attr-link-title">title</code> attribute of <var>element</var>.</p>
+      <p>The <code data-x="attr-link-title">title</code> attribute of <var>element</var>, if
+      <var>element</var> is <span>in a document tree</span>, or the empty string otherwise.</p>
 
       <p class="note">This is similarly a reference to the attribute, rather than a copy of the
       attribute's current value.</p>