libvpx: Pull from upstream

Current HEAD: 3431f575ed8338def631d51af93c36e6fce7dd07

git log from upstream:
55eaf58 Added Test vector that tests more show existing frames.
88ba088 Fix bug in error handling that causes segfault
815485a fix peek_si to enable 1 byte show existing frames.

BUG=386801
TBR=tomfinegan@chromium.org

Review URL: https://codereview.chromium.org/341343004

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/libvpx@278875 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
8 files changed