Sync-patch with libwebp ver 0.3.1 (Id: Idea3464b)

Change-Id: Ie2de5d5be3d7ec6020810f2d80530aa9d27e82c9
Update libwebp with patch for WebP-Animation.

Bug id for this change is 10512287

Omitted one libwebp patch that was added to Chrome
- f626fe2 Detect canvas and image size mismatch in decoder.
This patch added stricter check for matching the image width & height
and required more data to parse the header.
Since in Android, we use 64 byte buffer to parse the header, this change
was returning NOT_ENOUGH_DATA error while parsing WebP header.

Change-Id: Id73356a85ce1ceeeb822c1c428bf94b7127c6d0f
Fix memleak in WebPIDelete (change#Id4faef1b).

Corresponding bug for this fix is b/10823924

Happens when decoding is partial (past Partition0), without error and
interrupted by calling WebPIDelete()
WebPIDelete() needs to call VP8ExitCritical() to free in-flight
resources.

The upstream change for WebP has landed WebP git via gerrit patch:
https://gerrit.chromium.org/gerrit/#/c/67199/


Change-Id: Iae0fb5d1bd239f9641503f08ffb79780da7aa42f