gm: force all pixels opaque earlier in the process

gm: force all pixels opaque earlier in the process
Committed: https://code.google.com/p/skia/source/detail?r=7493

[epoger, 2013-01-31 16:22:09]

https://codereview.appspot.com/7251043/diff/1/gm/gmmain.cpp
File gm/gmmain.cpp (right):

https://codereview.appspot.com/7251043/diff/1/gm/gmmain.cpp#newcode1
gm/gmmain.cpp:1: /*
Toplevel comments:

Historically, gm has always forced all pixels opaque before writing the image
files out to disk.  This CL just does that EARLIER in the process, to simplify
in-memory image comparisons.  (Previously, we called force_all_opaque every time
we computed a checksum, to protect against this.)

This change will allow a cleaner implementation of
https://codereview.appspot.com/7238043/ ('output max-pixel-err if we're
comparing against known PNG files.')

https://codereview.appspot.com/7251043/diff/1/gm/gmmain.cpp#newcode321
gm/gmmain.cpp:321: * It's too bad that we are throwing away alpha channel data
this giant comment just moved here from the old get_checksum() method.

[reed1, 2013-01-31 16:23:39]

lgtm