Promote chrome.app.window alwaysOnTop property to stable unwhitelisted

This patch promotes the feature to stable for all apps.

BUG=314260
TEST=browser_tests (PlatformAppBrowserTest.WindowsApiAlwaysOnTop*)
Test manually using Window State sample app. Ensure the feature is
enabled for beta and stable builds.

Review URL: https://codereview.chromium.org/159523002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250659 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250659
Fix displaying of bookmark app dialog on Windows.

The dialog was being shown at ~150px width which is too small and wasn't
centered over the toolbar view. This CL sets the text field minimum width to
250 and the bubble's arrow to TOP_CENTER.

Although GetMinimumWidth is overridden, due to
crbug.com/342642, it isn't having the intended effect on
Windows.

BUG=331997

Review URL: https://codereview.chromium.org/157593008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250660 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250660