SkRemote: more refactoring

    - move Client / Server definitions to .cpp
    - rename Client / Server to Canvas / Decoder

No diffs:
https://gold.skia.org/search2?issue=1409113005&unt=true&query=source_type%3Dgm&master=false&include=true

BUG=skia:

Review URL: https://codereview.chromium.org/1409113005
3 files changed