Add pipe to core gyp project.
Do not run samplerstress through the pipe, since its
custom MaskFilter will not draw correctly.
Fix an assert in SkGPipeWrite when writing a typeface.
Review URL: https://codereview.appspot.com/6276044
git-svn-id: http://skia.googlecode.com/svn/trunk@4139 2bbb7eff-a529-9590-31e7-b0007b416f81