Fix vertical text alignment logic in canvas_skia.cc.
Fix vertical text alignment logic in canvas_skia.cc.

The previous code was not correctly calculating text
alignment. The new logic is much more intuitive and
also correct.

BUG=105550
TEST=Compare views_examples "Text Styles" examples
rendering between use_canvas_skia=1 and use_canvas_skia=0.

Review URL: http://codereview.chromium.org/9860042

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@129239 0039d316-1c4b-4281-b951-d872f2087c98

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