Remove WebFrame::canHaveSecureChild

To simplify the public API, ServiceWorkerNetworkProvider can do the
parent walk itself.

Follow-up to https://crrev.com/ad1850962644e19.

BUG=607543

Review-Url: https://codereview.chromium.org/2082493002
Cr-Commit-Position: refs/heads/master@{#400896}
Color Document::themeColor() const
{
    for (HTMLMetaElement* metaElement = head() ? Traversal<HTMLMetaElement>::firstChild(*head()) : 0; metaElement; metaElement = Traversal<HTMLMetaElement>::nextSibling(*metaElement)) {
        Color color = Color::transparent;
        if (equalIgnoringCase(metaElement->name(), "theme-color") && CSSParser::parseColor(color, metaElement->content().getString().stripWhiteSpace(), true))
            return color;
    }
    return Color();
}

Color Document::themeColor() const
{
    for (HTMLMetaElement* metaElement = head() ? Traversal<HTMLMetaElement>::firstChild(*head()) : 0; metaElement; metaElement = Traversal<HTMLMetaElement>::nextSibling(*metaElement)) {
        Color color = Color::transparent;
        if (equalIgnoringCase(metaElement->name(), "theme-color") && CSSParser::parseColor(color, metaElement->content().getString().stripWhiteSpace(), true))
            return color;
    }
    return Color();
}
