Use size_t for rowBytes.

Use size_t for rowBytes.

Previously, we were using uint32_t sometimes, int sometimes, and
size_t sometimes. Switch to using size_t, since we are actually
talking about a number of bytes.

In copyPixelsTo, use 0 as a flag to use the internal rowBytes,
which is more consistent with setConfig.

Committed: https://code.google.com/p/skia/source/detail?r=7843

[reed1, 2013-02-25 13:42:26]

lgtm