extend SkBenchmark to allow a bench to return a durationScale, which allows it to...

extend SkBenchmark to allow a bench to return a durationScale, which allows it to perform fewer actual interations, but report a scale factor to account for that. Thus a very slow bench can be compared head-to-head with a faster one, w/o actually forcing the tool to run for the full duration of the slower test.

Extend BitmapBench to time bicubic filtering, and use this durationScale for it.

Extend SkBenchmark to have setBitmapFlags(or, clear), allowing it to request a set of paint flags to be cleared, and set to be set.

BUG=
R=robertphillips@google.com

Review URL: https://codereview.chromium.org/16069010

git-svn-id: http://skia.googlecode.com/svn/trunk@9315 2bbb7eff-a529-9590-31e7-b0007b416f81