Make GrGLShaderBuilder::TextureSampler extract only required info from GrTextureAccess.

This will make it possible to init a TextureSampler without a texture or a specific config.

Also unify two separate bitfields of color components in GPU code.
Review URL: https://codereview.chromium.org/13121002

git-svn-id: http://skia.googlecode.com/svn/trunk@8428 2bbb7eff-a529-9590-31e7-b0007b416f81
17 files changed