Add animation support for WebP images

LayoutTests/fast/images/invalid-animated-webp.html

Index: LayoutTests/fast/images/invalid-animated-webp.html
diff --git a/LayoutTests/fast/images/invalid-animated-webp.html b/LayoutTests/fast/images/invalid-animated-webp.html
new file mode 100644
index 0000000000000000000000000000000000000000..b75ee2d9e3e98e40839f6e66e5a4a3d700fd324d
--- /dev/null
+++ b/LayoutTests/fast/images/invalid-animated-webp.html
@@ -0,0 +1,6 @@
+<script>
+if (window.testRunner)
+    window.testRunner.dumpAsText();
+</script>
+This test passes if no errors occur while decoding this large animation.<br>
+<img src="resources/webp-animated.webp">

[Noel Gordon, 2013/04/29 18:41:57]

This test should load resources/invalid-animated-webp.webp, right?  Also the
test should be a pixel test to check that we draw the broken-image icon.

[urvang (Google), 2013/04/30 13:14:15]

I believe this layout test is no longer needed, as we have a unit test now:
WEBPImageDecoderTest.cpp, which tests this.
Removing. Let me know if we still want this.

[Noel Gordon, 2013/05/01 17:55:28]

See below.