Make GrGLShaderBuilder check whether GrEffect advertised that it would require the dst color or fragment position

R=senorblanco@chromium.org, robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://chromiumcodereview.appspot.com/14998007

git-svn-id: http://skia.googlecode.com/svn/trunk@9074 2bbb7eff-a529-9590-31e7-b0007b416f81
10 files changed