[Mac] Update the warnings UI for malicious downloads.

[Mac] Update the warnings UI for malicious downloads.

When SafeBrowsing detects that a download is malicious, the user is only
presented with a 'Dismiss' option. Additional options ('Learn more' and
optionally 'Report', if applicable) are available from a context menu.

This behavior has been available on the Windows build. This change
brings the Mac UI up to parity.

XIB Changes (DownloadItem.xib):
* Add new controls for malicious downloads:
  * New GTMWidthBasedTweaker for managing the size of 'Dismiss' button
    connected to maliciousButtonTweaker: IBOutlet.
  * New 'Dismiss' push button connected to dismissMaliciousDownload:
    IBAction.
  * New disclosure button connected to showContextMenu: IBAction.
* Change connection for GTMWidthBasedTweaker containing 'Discard' button
  to dangerousButtonTweaker: IBOutlet.
* Anchor WidthBasedTweakers on the left instead of the right since the
  code assumes that the tweakers don't shift horizontally when the
  embedded buttons change size.
* Change height of Insecure Download NSBox to match the height of the
  DownloadItemButton.
* Adjust position of buttons for both dangerous and malicious downloads
  so that they are centered in the download shelf.

BUG=235931
TEST=(1) Download something from a URL that is identified by SafeBrowsing
         as malicious.
     (2) Check that the download shelf displays a warning indicating that
         the download was malicious and that it was blocked. There should
         only be a "Dismiss" button and a disclosure button.
     (3) Click on the disclosure button. It should display a menu with a
         'Learn more' item. Clicking on that item should open the
         SafeBrowsing help center article.
     (4) Click on the 'Dismiss' button. The warning should go away. If it
         was the only download, the shelf should also disappear.
     (5) Open chrome://downloads. The download should still be here with
         a 'Recover' option and a 'Remove' option.

Original Review URL: https://codereview.chromium.org/40733005/

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=232945

[asanka, 2013-11-04 20:17:25]

Hi Nico,

Could you take a quick look at this one? PS0 is identical to PS4 of
https://codereview.chromium.org/40733005/ which you reviewed last week. I've had
to re-upload it because the Base URL was busted in the previous CL. :-/

[asanka, 2013-11-04 20:20:18]

On 2013/11/04 20:17:25, asanka wrote:
> Hi Nico,
> 
> Could you take a quick look at this one? PS0 is identical to PS4 of
> https://codereview.chromium.org/40733005/ which you reviewed last week. I've
had
> to re-upload it because the Base URL was busted in the previous CL. :-/

Correction: PS1 of this CR is identical to PS4 of
https://codereview.chromium.org/40733005/.

[Nico, 2013-11-04 20:21:11]

lgtm stamp

[asanka, 2013-11-04 20:32:35]

On 2013/11/04 20:21:11, Nico wrote:
> lgtm stamp

Thanks!

[commit-bot: I haz the power, 2013-11-04 20:56:45]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/asanka@chromium.org/57963005/1

[commit-bot: I haz the power, 2013-11-05 01:23:01]

Retried try job too often on linux_aura for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_aura...

[commit-bot: I haz the power, 2013-11-05 02:39:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/asanka@chromium.org/57963005/1

[commit-bot: I haz the power, 2013-11-05 03:27:13]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/asanka@chromium.org/57963005/1

[commit-bot: I haz the power, 2013-11-05 07:25:32]

Change committed as 232945