Add more parameters to GrTextContext::canDraw

Updates canDraw to accept all the same Skia/Gr objects as the drawText
functions, since that information may very well be relevant in
determining whether a context can draw.

Also moves the onDrawTextBlob implementation directly into
drawTextBlob.

BUG=skia:

Review URL: https://codereview.chromium.org/1010113004
8 files changed