Misc cleanup

This is split off of https://codereview.chromium.org/1225923010/ (Start tightening correspondence betweeen GrDrawContext and GrRenderTarget). It:

fixes some style nits
replaces some passing of GrContext with GrTextureProvider & GrDrawContext
does a bit of the finer grained creation of GrDrawContexts

Review URL: https://codereview.chromium.org/1245183002
11 files changed