Fix use of wrong variable in ScrollBehaviorTest

LayoutTests/fast/scroll-behavior/resources/scroll-behavior-test.js

 // A ScrollBehaviorTest runs a set of ScrollBehaviorTestCases. The only
 // ScrollBehaviorTest method that should be called by external code is run().
 
 // Creates a ScrollBehaviorTest with arguments:
 // scrollElement - Element being scrolled.
 // scrollEventTarget - Target for scroll events for |scrollElement|.
 // testsCases - Array of ScrollBehaviorTestCases.
 // getEndPosition - Callback that takes a test case and start position, and
 //                  returns the corresponding end position (where positions
 //                  are dictionaries with x and y fields).
@@ skipping 16 matching lines @@
 }
 
 ScrollBehaviorTest.prototype.scrollListener = function(testCase) {
     if (testCase.waitForEnd) {
         if (this.scrollElement.scrollLeft == testCase.endX && this.scrollElement.scrollTop == testCase.endY)
             this.testCaseComplete();
         return;
     }
 
     // Wait for an intermediate frame, then instant-scroll to the end state.
-    if ((this.scrollElement.scrollLeft != testCase.startX || this.scrollElement.scrollTop != this.scrollElement.startY) &&
-        (this.scrollElement.scrollLeft != testCase.endX || this.scrollElement.scrollTop != this.scrollElement.endY)) {
+    if ((this.scrollElement.scrollLeft != testCase.startX || this.scrollElement.scrollTop != testCase.startY) &&
+        (this.scrollElement.scrollLeft != testCase.endX || this.scrollElement.scrollTop != testCase.endY)) {
         this.scrollElement.scrollLeft = {x: testCase.endX, behavior: "instant"};
         this.scrollElement.scrollTop = {y: testCase.endY, behavior: "instant"};
         this.testCaseComplete();
     }
 };
 
 ScrollBehaviorTest.prototype.startNextTestCase = function() {
     if (this.currentTestCase >= this.testCases.length) {
         this.allTestCasesComplete();
         return;
@@ skipping 12 matching lines @@
     testCase.setEndPosition(endPosition);
 
     this.scrollElement.style.scrollBehavior = testCase.css;
     this.jsScroll(testCase);
 
     var scrollElement = this.scrollElement;
     if (isSmoothTest) {
         this.asyncTest.step(function() {
             assert_equals(scrollElement.scrollLeft + ", " + scrollElement.scrollTop, testCase.startX + ", " + testCase.startY);
         });
-        testCase.scrollListener = this.scrollListener.bind(this, testCase);
-        this.scrollEventTarget.addEventListener("scroll", testCase.scrollListener);
+        if (scrollElement.scrollLeft == testCase.endX && scrollElement.scrollTop == testCase.endY) {
+            // We've instant-scrolled. This means we've already failed the assert above, and will never
+            // reach an intermediate frame. End the test case now to avoid hanging while waiting for an
+            // intermediate frame.
+            this.testCaseComplete();
+        } else {
+            testCase.scrollListener = this.scrollListener.bind(this, testCase);
+            this.scrollEventTarget.addEventListener("scroll", testCase.scrollListener);
+        }
     } else {
         this.asyncTest.step(function() {
             assert_equals(scrollElement.scrollLeft + ", " + scrollElement.scrollTop, testCase.endX + ", " + testCase.endY);
         });
         this.testCaseComplete();
     }
 }
 
 ScrollBehaviorTest.prototype.testCaseComplete = function() {
     var currentScrollListener = this.testCases[this.currentTestCase].scrollListener;
@@ skipping 35 matching lines @@
 
 ScrollBehaviorTestCase.prototype.setStartPosition = function(startPosition) {
     this.startX = startPosition.x;
     this.startY = startPosition.y;
 }
 
 ScrollBehaviorTestCase.prototype.setEndPosition = function(endPosition) {
     this.endX = endPosition.x;
     this.endY = endPosition.y;
 }