Make sure no more MIDI messages can be received after page unloads

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/17983003

git-svn-id: svn://svn.chromium.org/blink/trunk@153122 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Clean up some implementations of isKeyboardFocusable.

HTMLFormControlElement:
Checking existence of frame is redundant because renderer check in
isFocusable covers it. If the document has no frame, elements in the
document have no renderers.

HTMLSelectElement:
Because of the above change, HTMLFormControlElementWithState::
isKeyboardFocusable is just isFocusable. HTMLSelectElement::
isKeyboardFocusable adds nothing.

BUG=

Review URL: https://chromiumcodereview.appspot.com/18012002

git-svn-id: svn://svn.chromium.org/blink/trunk@153123 bbb929c8-8fbe-4397-9dbb-9b2b20218538