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

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

 /* This is the helper function to run animation tests:
 
 Test page requirements:
 - The body must contain an empty div with id "result"
 - Call this function directly from the <script> inside the test page
 
 Function parameters:
     expected [required]: an array of arrays defining a set of CSS properties that must have given values at specific times (see below)
     callbacks [optional]: a function to be executed immediately after animation starts;
                           or, an object in the form {time: function} containing functions to be
@@ skipping 357 matching lines @@
                     break;
             }
         }
     } else {
         var computedStyle = window.getComputedStyle(document.getElementById(elementId)).getPropertyCSSValue(property);
         if (computedStyle.cssValueType == CSSValue.CSS_VALUE_LIST) {
             var values = [];
             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;
                   case CSSValue.CSS_CUSTOM:
                     // arbitrarily pick shadow-x and shadow-y
                     if (property == 'box-shadow' || property == 'text-shadow') {
                       var text = computedStyle[i].cssText;
                       // Shadow cssText looks like "rgb(0, 0, 255) 0px -3px 10px 0px"
                       var shadowPositionRegExp = /\)\s*(-?\d+)px\s*(-?\d+)px/;
                       var match = shadowPositionRegExp.exec(text);
@@ skipping 311 matching lines @@
 
     [1] If the CSS property name is "-webkit-transform", expected value must be an array of 1 or more numbers corresponding to the matrix elements,
     or a string which will be compared directly (useful if the expected value is "none")
     If the CSS property name is "-webkit-transform.N", expected value must be a number corresponding to the Nth element of the matrix
 
 */
 function runTransitionTest(expected, trigger, callbacks, doPixelTest) {
     isTransitionsTest = true;
     runAnimationTest(expected, callbacks, trigger, false, doPixelTest);
 }