Managed preferences warning banner for Mac preferences dialog

Add a new view to the preferences dialog in Preferences.xib that holds the
alert image and the warning message label. Update the visibility of the warning
banner when switching preference views in PreferencesWindowController.

BUG=43423
TEST=none

Review URL: http://codereview.chromium.org/2831004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@50444 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index 4e8f2b0bb..3714b39 100755
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -902,6 +902,8 @@
         'browser/cocoa/ui_localizer.mm',
         'browser/cocoa/url_drop_target.h',
         'browser/cocoa/url_drop_target.mm',
+        'browser/cocoa/vertical_gradient_view.h',
+        'browser/cocoa/vertical_gradient_view.mm',
         'browser/cocoa/view_resizer.h',
         'browser/cocoa/web_contents_drag_source.h',
         'browser/cocoa/web_contents_drag_source.mm',