Remove obsolete comment in ShadowRoot.h

Source/core/dom/shadow/ShadowRoot.h

Index: Source/core/dom/shadow/ShadowRoot.h
diff --git a/Source/core/dom/shadow/ShadowRoot.h b/Source/core/dom/shadow/ShadowRoot.h
index 9024928cc1f48e64beffbfd23d728a8d40cea7fb..7832306e35bc50b21a5c89ca10a10a3840d2b9b4 100644
--- a/Source/core/dom/shadow/ShadowRoot.h
+++ b/Source/core/dom/shadow/ShadowRoot.h
@@ -49,10 +49,6 @@ class CORE_EXPORT ShadowRoot final : public DocumentFragment, public TreeScope,
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(ShadowRoot);
     friend class WTF::DoublyLinkedListNode<ShadowRoot>;
 public:
-    // FIXME: We will support multiple shadow subtrees, however current implementation does not work well

[hayato, 2015/06/04 07:25:07]

The spec dropped multiple shadow roots, however, Blink is still supporting
multiple shadow roots. Blink just deprecated it.
Instead of removing the comment, it looks it might be better to update the
comment.

[kochi, 2015/06/04 07:47:38]

What comment do you think is useful?

I think the problem this comment is about is what the GitHub issue#102
https://github.com/w3c/webcomponents/issues/102
covers, and the resolution is to throw exception where
createShadowRoot() cannot be done.

So there is something to do in implementation, but is it worth
referring to the GitHub issue here?

// TODO(hayato): throw exception on some elements which createShadowRoot()
// cannot work (e.g. <canvas>).
// See https://github.com/w3c/webcomponents/issues/102

or
// TODO(hayato): http://crbug.com/234020 make createShadowRoot() always work
// on all elements.

for longer-term solution (?).

WDYT?

[hayato, 2015/06/04 08:20:14]

Only part we have to remove is "We'll support multiple shadow subtrees", I
think. That's obsolete.

Other parts still have the status of the current implementation of multiple
shadow roots. We can't remove other comment for the reason which the description
of the CL says. We have to continue the support of multiple shadow roots for a
while.

-    // if a shadow root is dynamically created. So we prohibit multiple shadow subtrees
-    // in several elements for a while.
-    // See https://bugs.webkit.org/show_bug.cgi?id=77503 and related bugs.
     enum ShadowRootType {
         UserAgentShadowRoot = 0,
         OpenShadowRoot