Implement new maximize/restore button for CrOS behind the --ash-enable-alternate-caption-button flag

Notable changes:
- The new maximize/restore button does not show the help bubble when the mouse is hovered over the maximize/restore button
- The minimize and close buttons crossfade into buttons for snapping the window left and right respectively when a user clicks and holds the maximize/restore button

BUG=324596
TEST=AlternateFrameSizeButtonTest.*

Review URL: https://codereview.chromium.org/97613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239346 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239346
Implement a background downloader using BITS in Windows Chrome.
BUG=304354

Review URL: https://codereview.chromium.org/105853002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239347 0039d316-1c4b-4281-b951-d872f2087c98
[telemetry] Print [ OK ] on skipped tests, the same as we do for successes.


BUG=326672
TEST=I'm sure the trybots have got it covered.

Review URL: https://codereview.chromium.org/108353006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239348 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239348
Makes several fixes and enhancements to ChromeVox load/unload.

- Ensure ChromeVox loads to user screen while on locked screen to read status tray.
- fix crashy behavior with registered observers.
- keep tighter track of ChromeVox's lifetime via extension_* notifications.

BUG=321864
TEST=Run through the following scenarios:
- enable/disable on lock screen via ctrl+alt+z
- OOBE flow.
- lock with ChromeVox on
- unlock with ChromeVox on

Review URL: https://codereview.chromium.org/82553013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239349 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239349