Factor addReferenceTo()-calls out of SVGUseElement::buildShadowTree

Factor addReferenceTo()-calls out of SVGUseElement::buildShadowTree

This factors the registering of references to first degree nested <use>
elements out of the buildShadowTree, getting rid of the |foundUse|
parameter. This brings us one step closer to more streamlined shadow-
tree construction. It also avoids calling isStructurallyExternal() more
than once.

Also cleanup the instanceTreeIsLoading() method by letting it traverse
all the SVGUseElement descendants of the shadow root using the
Traversal<> helpers.

BUG=589682
Committed: https://crrev.com/e2422a52e0a68ea44f57cf9446408c8e6e311425
Cr-Commit-Position: refs/heads/master@{#379289}

[fs, 2016-03-04 13:56:59]

fs@opera.com changed reviewers:
+ pdr@chromium.org, schenney@chromium.org

[Stephen Chennney, 2016-03-04 15:21:43]

LGTM

[fs, 2016-03-04 15:31:04]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2016-03-04 15:31:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1759423003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1759423003/1

[Stephen Chennney, 2016-03-04 15:31:58]

The CQ bit was unchecked by schenney@chromium.org

[Stephen Chennney, 2016-03-04 15:34:35]

Sorry, not LGTM due to some confusion on my part. If using
Traversal<SVGUseElement>::nextSkippingChildren, how to we get the same recursive
behavior we have with buildInstanceTree?

[Stephen Chennney, 2016-03-04 15:35:59]

On 2016/03/04 15:34:35, Stephen Chenney wrote:
> Sorry, not LGTM due to some confusion on my part. If using
> Traversal<SVGUseElement>::nextSkippingChildren, how to we get the same
recursive
> behavior we have with buildInstanceTree?

Answered my own question. We weren't recursing before due to the "foundUse"
argument.

LGTM again and I'll CQ.

[Stephen Chennney, 2016-03-04 15:36:10]

The CQ bit was checked by schenney@chromium.org

[commit-bot: I haz the power, 2016-03-04 15:36:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1759423003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1759423003/1

[commit-bot: I haz the power, 2016-03-04 15:41:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-04 15:43:24]

Description was changed from

==========
Factor addReferenceTo()-calls out of SVGUseElement::buildShadowTree

This factors the registering of references to first degree nested <use>
elements out of the buildShadowTree, getting rid of the |foundUse|
parameter. This brings us one step closer to more streamlined shadow-
tree construction. It also avoids calling isStructurallyExternal() more
than once.

Also cleanup the instanceTreeIsLoading() method by letting it traverse
all the SVGUseElement descendants of the shadow root using the
Traversal<> helpers.

BUG=589682
==========

to

==========
Factor addReferenceTo()-calls out of SVGUseElement::buildShadowTree

This factors the registering of references to first degree nested <use>
elements out of the buildShadowTree, getting rid of the |foundUse|
parameter. This brings us one step closer to more streamlined shadow-
tree construction. It also avoids calling isStructurallyExternal() more
than once.

Also cleanup the instanceTreeIsLoading() method by letting it traverse
all the SVGUseElement descendants of the shadow root using the
Traversal<> helpers.

BUG=589682

Committed: https://crrev.com/e2422a52e0a68ea44f57cf9446408c8e6e311425
Cr-Commit-Position: refs/heads/master@{#379289}
==========

[commit-bot: I haz the power, 2016-03-04 15:43:25]

Patchset 1 (id:??) landed as
https://crrev.com/e2422a52e0a68ea44f57cf9446408c8e6e311425
Cr-Commit-Position: refs/heads/master@{#379289}

[fs, 2016-03-04 15:46:59]

On 2016/03/04 at 15:34:35, schenney wrote:
> Sorry, not LGTM due to some confusion on my part. If using
Traversal<SVGUseElement>::nextSkippingChildren, how to we get the same recursive
behavior we have with buildInstanceTree?

We don't want to descend into any subtree (full or partial) that is rooted in an
SVGUseElement - this is what the |foundUse| parameter was used for in
buildShadowTree (i.e when set to 'true' we'd skip the check for all descendants
of the SVGUseElement).

So the recursive formulation would be:

void addRef...(SVGElement& target)
{
    if (isSVGUseElement(target)) {
        addReferenceTo(target);
        return;
    }
    for (SVGElement& child : childrenOf(target))
        addRef...(child);
}

which should amount to a pre-order traversal with "subtree pruning".

Not sure if that helps, but essentially:

When a <use> is seen, add a reference and continue with its next sibling - if
none walk the ancestors chain until one sibling is found (or we reached the
root)

in text form. I believe this describes nextSkippingChildren pretty well, and
hence why it's a perfect fit.