Downsample thumbnail by powers of two before doing lanczos
Downsample thumbnail by powers of two before doing lanczos

This speeds up the resizing portion of thumbnailing from 40ms->15ms on my linux z600 at nearly fullscreen resolution.  Thumbnail resizing times on weaker hardware (like netbooks) has been observed in the 150ms+ range, so hopefully this is a proportional speedup there as well.

TEST=none
BUG=62820

Review URL: http://codereview.chromium.org/4846002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@65982 0039d316-1c4b-4281-b951-d872f2087c98

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