cros: Don't let v2 apps block the brightness and volume system keys

Previously system hardware keys were passed to both v1 and v2 apps. Poorly behaved apps could then consume those keys and prevent the user from changing the volume.

This patch makes the system hardware keys be handled by default in the ash layer. However, because some legacy v1 apps still expect those key events we allow v1 apps to continue to receive them via a window state setting.

This paves the way for a v2 app permission to request access to these keys, see issue 166928.

BUG=281761
TEST=ash_unittests, also launch app "Keyboard Handler Sample"[1] and volume keys should still control volume. [1] https://chrome.google.com/webstore/detail/keyboard-handler-sample/pcbbaldjljokfnnkphllabnpolciapjc

Review URL: https://codereview.chromium.org/25372006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226645 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226645
A browwer window should be activatable unless the modal dialog is actually shown

BUG=302002
R=sky@chromium.org

Review URL: https://codereview.chromium.org/25411006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226646 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226646