WebPDecoder: Remove backward emulation for old libwebp versions

The backward emulation was required in WebKit, due to different ports
using different libwebp versions.
This is no longer rquired in Blink.

BUG=

Review URL: https://chromiumcodereview.appspot.com/18242002

git-svn-id: svn://svn.chromium.org/blink/trunk@153287 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rename various variables and arguments to match the naming from the spec

This should make it easier to understand the code. I have also
simplified some calculations and gave some expressions their own
variables.

R=ojan@chromium.org
BUG=249551

Review URL: https://chromiumcodereview.appspot.com/18052028

git-svn-id: svn://svn.chromium.org/blink/trunk@153288 bbb929c8-8fbe-4397-9dbb-9b2b20218538
bindings: Add a test for checking the correctness of generated EventNames.in

This is a follow-up for r153210.

BUG=none
R=abarth@chromium.org, ch.dumez@sisa.samsung.com

Review URL: https://codereview.chromium.org/18052021

git-svn-id: svn://svn.chromium.org/blink/trunk@153289 bbb929c8-8fbe-4397-9dbb-9b2b20218538