Issue 92. New tests for cairo

Hi Bryce,
I added new canvas performance tests to cairo stubs similar to skia. The changes are tested. Please find the following note about the changes.
1. generate_test script doesn't seems to work fine for image-scale, image-rotate case as extra '-' is there.
2. Changes in cairo-shapes.cpp and skia-shapes.cpp cairoDrawLine, cairoDrawQuadraticCurve are made so that skia and cairo outputs are same. 
3. For image-scale case it seems there is no direct API in cairo like skia's drawBitmapRect(). So i used translate-scale method. Need your comments on this. 
4. Some cases like skia-image-rotate and skia-image-scale crashes in PC. So I am not able to compare the outputs with skia. Need to check in device once. Is the crash happens in your environment also ?
5. Output of star case in cairo and skia for hairline stroke is little bit different. 

Thanks,
Suyambu