Fix race conditions in animations/transitions tests.

These tests were all kicking off an animation/transition before the
first recalc was guaranteed to happen. Mostly the tests happen to work,
but they break when we turn on lazy attaching from the parser.

Review URL: https://chromiumcodereview.appspot.com/23461011

git-svn-id: svn://svn.chromium.org/blink/trunk@156815 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Collapse Gamepads.h and remove modules/gamepad/ from core/DEPS

BUG=

Review URL: https://chromiumcodereview.appspot.com/23495002

git-svn-id: svn://svn.chromium.org/blink/trunk@156816 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Clean up DocumentType now that it always has a Document

DocumentType always has an ownerDocument now so we can clean up its
insertedInto and removedFrom callbacks.

When I was cleaning this up I also realized that DocumentType::entities() and
notations() always return null and were removed in DOM4 so we can remove their
storage from DocumentType.

Review URL: https://chromiumcodereview.appspot.com/23534003

git-svn-id: svn://svn.chromium.org/blink/trunk@156818 bbb929c8-8fbe-4397-9dbb-9b2b20218538