Round the scroll offset synced back to main instead of flooring.

third_party/WebKit/LayoutTests/fast/scroll-behavior/resources/scroll-interruption-test.js

 // A SmoothScrollInterruptionTest verifies that in-progress smooth scrolls
 // stop when interrupted by an instant scroll, another smooth scroll, a
 // touch scroll, or a mouse wheel scroll.
 //
 // The only SmoothScrollInerruptionTest method that should be called by
 // outside code is run().
 //
 // Creates a SmoothScrollInterruptionTest with arguments:
 // scrollElement - Element being scrolled.
 // innerPoint - Absolute position (expressed as a dictionary with x and y fields)
@@ skipping 29 matching lines @@
         return;
     }
 
     var testCase = this.testCases[this.currentTestCase];
     this.asyncTest = async_test(testCase.description);
 
     var scrollElement = this.scrollElement;
     var scrollStartPoint = this.scrollStartPoint;
 
     scrollElement.scrollTop = scrollStartPoint;
-    window.requestAnimationFrame(this.performSmoothScroll.bind(this));
+    window.requestAnimationFrame(this.waitForSyncScroll.bind(this));
+}
+
+SmoothScrollInterruptionTest.prototype.waitForSyncScroll = function() {
+  // Wait until cc has received the commit from main with the scrollStartPoint.
+  if (this.scrollElement.scrollTop != this.scrollStartPoint) {
+    // TODO(flackr): There seems to be a bug in that we shouldn't have to
+    // reapply the scroll position when cancelling a smooth scroll.
+    // https://crbug.com/667477
+    this.scrollElement.scrollTop = this.scrollStartPoint;
+    window.requestAnimationFrame(this.waitForSyncScroll.bind(this));
+    return;
+  }
+
+  this.performSmoothScroll();
 }
 
 SmoothScrollInterruptionTest.prototype.performSmoothScroll = function() {
     var testCase = this.testCases[this.currentTestCase];
     var scrollElement = this.scrollElement;
     var scrollStartPoint = this.scrollStartPoint;
 
     this.jsScroll(this.scrollEndPoint);
     this.asyncTest.step(function() {
         assert_equals(scrollElement.scrollTop, scrollStartPoint);
@@ skipping 122 matching lines @@
 }
 
 function interruptWithWheelScroll(smoothScrollTest) {
     if (window.eventSender) {
         window.eventSender.mouseMoveTo(smoothScrollTest.innerPoint.x, smoothScrollTest.innerPoint.y);
         window.eventSender.mouseScrollBy(0, -10);
     } else {
         document.write("This test does not work in manual mode.");
     }
 }