Implement support for unprefixed keyframes rules resolution.

Source/core/css/CSSKeyframesRule.cpp

Index: Source/core/css/CSSKeyframesRule.cpp
diff --git a/Source/core/css/CSSKeyframesRule.cpp b/Source/core/css/CSSKeyframesRule.cpp
index 80c69288d767fb8ab6fdd23681a90c63815a49c3..b4fbb0e3d996795b3b67315c4c5d3c3585880b38 100644
--- a/Source/core/css/CSSKeyframesRule.cpp
+++ b/Source/core/css/CSSKeyframesRule.cpp
@@ -43,6 +43,7 @@ StyleRuleKeyframes::StyleRuleKeyframes(const StyleRuleKeyframes& o)
     : StyleRuleBase(o)
     , m_keyframes(o.m_keyframes)
     , m_name(o.m_name)
+    , m_isPrefixed(o.m_isPrefixed)
 {
 }
 
@@ -88,6 +89,7 @@ CSSKeyframesRule::CSSKeyframesRule(StyleRuleKeyframes* keyframesRule, CSSStyleSh
     : CSSRule(parent)
     , m_keyframesRule(keyframesRule)
     , m_childRuleCSSOMWrappers(keyframesRule->keyframes().size())
+    , m_isPrefixed(keyframesRule->isVendorPrefixed())
 {
 }
 
@@ -151,7 +153,10 @@ CSSKeyframeRule* CSSKeyframesRule::findRule(const String& s)
 String CSSKeyframesRule::cssText() const
 {
     StringBuilder result;
-    result.append("@-webkit-keyframes ");
+    if (isVendorPrefixed())
+        result.append("@-webkit-keyframes ");
+    else
+        result.append("@keyframes ");
     result.append(name());
     result.append(" { \n");