Enable encrypted cookies on Mac OSX.

Encrypted cookies have been enabled on Windows and Linux for some time but Mac needed to be done separately because tests will hang unless the Encryptor is first told to use the mock keychain.

BUG=313323

Review URL: https://codereview.chromium.org/135183021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250568 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250568
Fixes crash during destruction

During tear down the ActivationClient may be NULL. NativeWidgetAura
needs to check appropriately before using ActivationClient.

BUG=314118 342529
TEST=covered by test now
R=ben@chromium.org

Review URL: https://codereview.chromium.org/159503002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250569 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250569