Merge WebP at 0.4.1-rc1, plus MIPS build fixes.

These changes have landed to the system copy of libwebP in
Idf2756b8881d10001c0663bca454aac86ab30a39

and this brings the WebView version in line with it.

Bug: 17028120
Change-Id: I9e150225d7fb8e280cb1e632dc184191ed94fae8
137 files changed