Add a tiled pipe mode to SampleApp.

Add a tiled pipe mode to SampleApp.

Using the "Pipe" checkbox in SamleApp, you can now
toggle amongst three states: no pipe, a normal pipe
(or others depending on #defines), and a tiled pipe.
You can also use shift + p to toggle.
Review URL: https://codereview.appspot.com/6303055

git-svn-id: http://skia.googlecode.com/svn/trunk@4213 2bbb7eff-a529-9590-31e7-b0007b416f81