printer: Expose printer to user through proxy

User can use printer directly after getting chameleon proxy p.
e.g.
p.printer.Plug()

p.printer.SetPrinterModel(1008, 17, 'hp officejet g55')

p.printer.StartCapturingPrinterData()

p.printer.StopCapturingPrinterData()

p.printer.Reset()

p.Reset()

BUG=chromium:787414
TEST=Use test_server to set printer model and add printer in chrome://settings.
     Print an example PDF file and check the md5sum is always the same
     for a printer model.
Change-Id: Ibdb886cfa1859c924d6781ec8fd2c56daf1a1897
Reviewed-on: https://chromium-review.googlesource.com/952733
Commit-Ready: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Wai-Hong Tam <waihong@google.com>
Reviewed-by: Kalin Stoyanov <kalin@chromium.org>
2 files changed