Issue 112. Add SkDeferredCanvas to caskbench.

Hi Bryce, 
i. I have added SkDeferredCanvas to caskbench and made changes to use latest skia branches(dev/m36_1985/henry). 
ii. Also made minor modifications to canvas_perf script. If gles warnings are thrown, the script assumes those also as json output and it breaks. 
Kindly review the code and let me know if any improvements can be done.

Thanks,
Suyambu