Cargo cult gif tests to webp this time: https://codereview.chromium.org/2786883006

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/79580105235657014da58d4a36ca170fd4e63ff9

commit 79580105235657014da58d4a36ca170fd4e63ff9
Author: noel <noel@chromium.org>
Date: Fri Mar 31 16:08:36 2017

Add paint invalidation tests for animated WEBP images

Add an animated WEBP image resource derived from the GIF resource
and add invalidation tests for the basic image case, when it is a
CSS background image, and when it positioned off-screen.

BUG= 707178 

Review-Url: https://codereview.chromium.org/2786883006
Cr-Commit-Position: refs/heads/master@{#461137}

[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/fast/backgrounds/resources/red-green-animated.webp
[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/paint/invalidation/animated-webp-background-expected.txt
[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/paint/invalidation/animated-webp-background.html
[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/paint/invalidation/animated-webp-expected.txt
[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/paint/invalidation/animated-webp-offscreen-expected.txt
[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/paint/invalidation/animated-webp-offscreen.html
[add] https://crrev.com/79580105235657014da58d4a36ca170fd4e63ff9/third_party/WebKit/LayoutTests/paint/invalidation/animated-webp.html