Added a new function to directly generate a blurred rectangle analytically.

Added two new microbenchmarks to demonstrate speedup over existing BlurSeparable approach.

Added new GM tests for blurred rectangles. 
Review URL: https://codereview.appspot.com/7037050

git-svn-id: http://skia.googlecode.com/svn/trunk@7034 2bbb7eff-a529-9590-31e7-b0007b416f81
9 files changed