Fix SkGifCodec to handle gifs where frameSize != imageSize

These are quite rare, causing us to miss a few bugs in how
we deal with these images.

Additionally, there is a behavior change.  If the imageSize
is not large enough to contain the frame, we will "fix" the
image by increasing the image size.

SkScaledCodec is still buggy with regard to these gifs.
See skbug.com/4421. We will fix that after 1332053002
lands.

BUG=skia:

Review URL: https://codereview.chromium.org/1386973002
2 files changed