Avoid crash on some 64b ARM NEON platforms.

The compiler may choose to use x30 for a local loop counter;
ensure it's saved. Patch from kevin.petit@arm.com,
verified by benm@google.com.

R=djsollen@google.com

Review URL: https://codereview.chromium.org/786273003
Rebaselines for https://codereview.chromium.org/785893004/ (Fix MatrixImageFilter computeFastBounds)

The msaa4 image diffs aren't actually due to the named CL

TBR=scroggo@google.com

Review URL: https://codereview.chromium.org/787093002
Replace EncodeBitmap with an interface.

Gives more flexibility to the caller to decide whether to use the
encoded data returned by refEncodedData().

Provides an implementation that supports the old version of
SkPicture::serialize().

TODO: Update Chrome, so we can remove SK_LEGACY_ENCODE_BITMAP entirely

BUG=skia:3190

Committed: https://skia.googlesource.com/skia/+/0c4aba6edb9900c597359dfa49d3ce4a41bc5dd1

Review URL: https://codereview.chromium.org/784643002
Revert of Replace EncodeBitmap with an interface. (patchset #12 id:210001 of https://codereview.chromium.org/784643002/)

Reason for revert:
Failing serialization tasks in DM:

http://build.chromium.org/p/client.skia/builders/Test-Win8-ShuttleA-GTX660-x86-Debug/builds/352/steps/dm/logs/stdio

Original issue's description:
> Replace EncodeBitmap with an interface.
>
> Gives more flexibility to the caller to decide whether to use the
> encoded data returned by refEncodedData().
>
> Provides an implementation that supports the old version of
> SkPicture::serialize().
>
> TODO: Update Chrome, so we can remove SK_LEGACY_ENCODE_BITMAP entirely
>
> BUG=skia:3190
>
> Committed: https://skia.googlesource.com/skia/+/0c4aba6edb9900c597359dfa49d3ce4a41bc5dd1
>
> Committed: https://skia.googlesource.com/skia/+/02b217f80b01a7dda8493422e5257c36a9ce8464

TBR=reed@google.com,rmistry@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:3190

Review URL: https://codereview.chromium.org/783393004