Revert of Update libwebp and resume testing scaled webp (patchset #2 id:20001 of https://codereview.chromium.org/1280073002/ )

Reason for revert:
Compile failures, e.g.

http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-Arm7-Debug-Android_NoNeon/builds/1427/steps/build%20most/logs/stdio

Original issue's description:
> Update libwebp and resume testing scaled webp
>
> libwebp has a fix for [1]. Update to the commit that contains the fix.
>
> Update libwebp.gypi, corresponding to libwebp's latest makefile.
>
> Turn back on DM testing for scaled webp, now that it should no longer
> use uninitialized memory.
>
> Fix a warning in config.h
>
> [1] https://code.google.com/p/webp/issues/detail?id=254
>
> BUG=skia:4038
>
> Committed: https://skia.googlesource.com/skia/+/0575d3e6c272744a66ab3281f9871366717df339

TBR=djsollen@google.com,msarett@google.com,scroggo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:4038

Review URL: https://codereview.chromium.org/1278173004
4 files changed