HTMLMediaElement::createMediaControls should use AttachLazily

The media element UI controls should be attached lazily.

TBR=eseidel

Review URL: https://chromiumcodereview.appspot.com/23224011

git-svn-id: svn://svn.chromium.org/blink/trunk@156349 bbb929c8-8fbe-4397-9dbb-9b2b20218538