Remove ambiguous operator= on AutoCFRelease.

Remove ambiguous operator= on AutoCFRelease.

The operator= is ambiguous as to the state of the reference count.
Until we have rvalue assignment operators, just use 'reset' as the name
of the reference stealing assignment to AutoCFRelease.

Committed: https://skia.googlesource.com/skia/+/e194c495e95cbe92dfb9ed04515904a417fe7e9b

[bungeman-skia, 2014-07-16 19:48:47]

This is a continuation of the CGBitmap leak CL which went in earlier. The idea
is to remove the ambiguity of operator= on reference count maintaining auto
pointers.

[mtklein, 2014-07-16 20:21:53]

lgtm

[commit-bot: I haz the power, 2014-07-16 20:22:59]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/bungeman@google.com/400453002/1

[commit-bot: I haz the power, 2014-07-16 20:46:14]

Change committed as e194c495e95cbe92dfb9ed04515904a417fe7e9b