Mac: Try to fix a crash related to save panels.

All the stacks are always in the destructors. Wild guess: Maybe NSSavePanel takes the context object from the delegate instead of self. Pass in the delegate as described by the docs.

BUG=58959
TEST=maybe fewer crashes on the crash server

Review URL: http://codereview.chromium.org/6031008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70265 0039d316-1c4b-4281-b951-d872f2087c98