[HEAD BROKEN] Rename \Drupal\Core\Render\Element\Html to avoid namespace clash with \Drupal\Component\Utility\Html in render elements.

My latest head with latest drush si, PHP 5.4.30 failed with:
PHP Fatal error: Cannot use Drupal\Component\Utility\Html as Html because the name is already in use in /usr/local/var/www/d8.dev/www/core/lib/Drupal/Core/Render/Element/Link.php on line 11

Works again after applying the patch.

I don't understand how this is a bug, but either way, let's just do this.

Credit should also go to neclimdul for spending a lot of time on this in IRC

Patch #3 works for me.

RTBC+

This is the bug:

http://3v4l.org/PCmhc

namespace A {
    class Foo {
    }
}
namespace A {
    use B\Foo;
    class Bar {
        function __construct() { 
            new Foo();
        }
    }
}
namespace B {
    class Foo {
    }
}

Fatal error: Cannot use B\Foo as Foo because the name is already in use in /in/PCmhc on line 8

Process exited with code 255.

I would expect this to work, especially if each namespace were split across three files.

ircmaxell confirmed this is a bug in all versions of PHP.
http://lxr.php.net/xref/PHP_5_5/Zend/zend_compile.c#7039

I'm guessing the testbots use opcache, because that's the only way they'd pass:

The reason it works with opcache is that opcache removes the symbol table at compile time. So there is never a conflict

ircmaxell said he'd file a PHP7 bug report tomorrow.

In the interest of getting this committed, I'm taking #5 as an RTBC.

Added suggested commit message to summary.

Similar issue: #2420421: HEAD BROKEN: Fatal error: Cannot use Drupal\Component\Utility\Xss as Xss because the name is already in use in /var/lib/drupaltestbot/sites/default/files/checkout/core/modules/views/src/Plugin/views/field/Field.php on line 11

The patch was reverted.