Update for Shadow DOM

See discussion about this change at:
WICG/webcomponents#192

Splits Document.pointerLockElement into Document.pointerLockElement and
ShadowRoot.pointerLockElement and encapsulates shadow tree from
document.

Other than split, replaces document to 'shadow-including document' where
necessary.

index.html

@@ -239,9 +239,9 @@ <h2>Extensions to the <a>Element</a> Interface</h2>
           active sandboxing flag set</a> does not have the <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/origin-0.html#sandboxed-pointer-lock-browsing-context-flag">
           sandboxed pointer lock browsing context flag</a> set.
 
-          <p>Pointer lock must succeed only if the <a>target</a> is
-          <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#in-a-document">in</a>
-          the
+          <p>Pointer lock must succeed only if the <a>target</a>'s
+          <a href="https://dom.spec.whatwg.org/#concept-shadow-including-root">shadow-including root</a>
+          is the
           <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#active-document">active document</a>
           of a
           <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing context</a>
@@ -275,12 +275,13 @@ <h2>Extensions to the <a>Element</a> Interface</h2>
             for a subsequent requestPointerLock.
           </p>
 
-          <p>If any element (including this one) in the same document
+          <p>If any element (including this one) in the same shadow-including document
           is already locked (or pending lock) the pointer
           lock <a>target</a> must be updated to this element and a
           <a>pointerlockchange</a> event sent.</p>
 
-          <p>If any element in another document is already locked the request
+          <p>If any element whose <a href="https://dom.spec.whatwg.org/#concept-shadow-including-root">shadow-including root</a> is a different document
+          is already locked the request
           must fail and a <a>pointerlockerror</a> event be sent.</p>
 
           <p>Once in the locked state the <a>user agent</a> must fire all relevant
@@ -322,21 +323,12 @@ <h2>Extensions to the <a>Document</a> Interface</h2>
           for <a>pointerlockerror</a> events.</p>
         </dd>
 
-        <dt>readonly attribute Element? pointerLockElement</dt>
-        <dd>
-          <dfn title="pointerLockElement"></dfn>
-
-          <p>Returns the element set as the <a>target</a> for mouse events
-          while the pointer is locked. Null if lock is pending, pointer is
-          unlocked, or if the target is in another document.</p>
-        </dd>
-
         <dt>void exitPointerLock ()</dt>
         <dd>
           <dfn title="exitPointerLock"></dfn>
 
           <p>Initiates an exit from pointer lock state if currently locked
-          to a target in this document,
+          to a target whose <a href="https://dom.spec.whatwg.org/#concept-shadow-including-root">shadow-including root</a> is this document,
           and sends a <a>pointerlockchange</a> event when the lock state
           has been exited.</p>
 
@@ -348,6 +340,24 @@ <h2>Extensions to the <a>Document</a> Interface</h2>
       </dl>
     </section>
 
+    <section>
+      <h2>Extensions to the <a>DocumentOrShadowRoot</a> Mixin</h2>
+
+      <dl title='partial interface DocumentOrShadowRoot' class='idl'>
+         <dt>readonly attribute Element? pointerLockElement</dt>
+         <dd>
+           <dfn title="pointerLockElement"></dfn>
+
+           <p>Returns the result of the
+           <a href="https://w3c.github.io/webcomponents/spec/shadow/#dfn-retargeting-algorithm">retargeting algorithm</a>
+           with the <a href="http://dom.spec.whatwg.org/#context-object">context object</a>
+           and the element set as the <a>target</a> for mouse events
+           while the pointer is locked. Null if lock is pending, pointer is
+           unlocked, or if the target's <a href="https://dom.spec.whatwg.org/#concept-shadow-including-root">shadow-including root</a> is a different document.</p>
+         </dd>
+      </dl>
+    </section>
+
     <section>
       <h2>Extensions to the <a>MouseEvent</a> Interface</h2>
 
@@ -430,7 +440,8 @@ <h2>Requirements</h2>
       [[FULLSCREEN]].</p>
 
       <p>Pointer lock must be exited if the
-      <a>target</a> is removed from its document, or the <a>user agent</a>,
+      <a>target</a> is <a href="https://html.spec.whatwg.org/#node-is-disconnected">disconnected</a>,
+      or the <a>user agent</a>,
       window, or tab loses focus. Moving focus between elements of
       <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#active-document">active documents</a>,
       including between