Implement support for unprefixed keyframes rules resolution.

LayoutTests/animations/duplicated-keyframes-name-unprefixed-01.html

Index: LayoutTests/animations/duplicated-keyframes-name-unprefixed-01.html
diff --git a/LayoutTests/animations/duplicated-keyframes-name.html b/LayoutTests/animations/duplicated-keyframes-name-unprefixed-01.html
similarity index 93%
copy from LayoutTests/animations/duplicated-keyframes-name.html
copy to LayoutTests/animations/duplicated-keyframes-name-unprefixed-01.html
index 1ab642c159289d78f96f5d9387f6e7d07d59a9aa..fbe9df9d045cdf8e6930838d61e5f08bd5af81ce 100644
--- a/LayoutTests/animations/duplicated-keyframes-name.html
+++ b/LayoutTests/animations/duplicated-keyframes-name-unprefixed-01.html
@@ -18,15 +18,15 @@
         -webkit-animation-name: anim;
         -webkit-animation-fill-mode: forwards;
     }
-    @-webkit-keyframes anim {
+    @keyframes anim {
         from { left: 50px; }
         to   { left: 100px; }
     }
-    @-webkit-keyframes irrelevant {
+    @keyframes irrelevant {
         from { left: 150px; }
         to   { left: 2500px; }
     }
-    @-webkit-keyframes anim {
+    @keyframes anim {
         from { left: 200px; }
         to   { left: 300px; }
     }