10.6 SDK compatibility fix for DockIcon following r37698.
10.6 SDK compatibility fix for DockIcon following r37698.

See r26348, "Avoid spurious errors about NSColor*-CGColor* and NSSize-CGSize
conversions": The SDK has gotten stupider in 10.6, and has conspired with the
compiler, which now thinks that when the receiver is held in a scoped_nsobject,
NSColor and NSSize arguments should be converted to their CG cousins.

BUG=35569
TEST=10.6 SDK build (mac_sdk=10.6)
Review URL: http://codereview.chromium.org/606027

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@38956 0039d316-1c4b-4281-b951-d872f2087c98

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