Use 4 value syntax for getComputedStyle of background-position and -webkit-mask-position

LayoutTests/animations/resources/animation-test-helpers.js

Index: LayoutTests/animations/resources/animation-test-helpers.js
diff --git a/LayoutTests/animations/resources/animation-test-helpers.js b/LayoutTests/animations/resources/animation-test-helpers.js
index 2811a69bb31ac344aabebc2193a1cef2ed30ec86..9dbde7e1682c01ac1c7dc8e65deeafa7be67ad78 100644
--- a/LayoutTests/animations/resources/animation-test-helpers.js
+++ b/LayoutTests/animations/resources/animation-test-helpers.js
@@ -375,8 +375,10 @@ function checkExpectedTransitionValue(expected, index)
             for (var i = 0; i < computedStyle.length; ++i) {
                 switch (computedStyle[i].cssValueType) {
                   case CSSValue.CSS_PRIMITIVE_VALUE:
-                    if (computedStyle[i].primitiveType == CSSPrimitiveValue.CSS_STRING)
+                    if (computedStyle[i].primitiveType === CSSPrimitiveValue.CSS_STRING)
                         values.push(computedStyle[i].getStringValue());
+                    else if (computedStyle[i].primitiveType === CSSPrimitiveValue.CSS_IDENT)
+                        values.push(computedStyle[i].cssText);
                     else
                         values.push(computedStyle[i].getFloatValue(CSSPrimitiveValue.CSS_NUMBER));
                     break;