mac: Fix HighDPI mode on 10.7.3
mac: Fix HighDPI mode on 10.7.3

Apparently omission of the NSPrincipalClass key sends an app down
the magnify mode path starting with 10.7.3. Thanks to
YAMAMOTO Mitsuharu for figuring this out:

http://lists.gnu.org/archive/html/emacs-devel/2012-03/msg00052.html

BUG=31960
TEST=Start chromium in highdpi mode. Toolbar looks good.
NOTRY=true

Review URL: http://codereview.chromium.org/10069029

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@132117 0039d316-1c4b-4281-b951-d872f2087c98

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