ninja/mac: Add extra plist item DTPlatformVersion and DTPlatformBuild.

Without DTPlatformVersion iOS apps on iOS7 have a weird black bar, and
don't show the snapshot on backgrounding and foregrounding

Without DTPlatformBuild Xcode instruments won't load apps at all.

BUG=None
TEST=None
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/40963003

git-svn-id: http://gyp.googlecode.com/svn/trunk@1770 78cadc50-ecff-11dd-a971-7dbc132099af