Deflake repaint layout tests which assumed scroll would happen before first paint.

LayoutTests/fast/repaint/resources/text-based-repaint.js

 // Asynchronous tests should manually call finishRepaintTest at the appropriate
 // time.
 window.testIsAsync = false;
 window.outputRepaintRects = true;
 window.generateMinimumRepaint = false; // See comments about 'Minimum repaint' below.
 
 function runRepaintTest()
 {
     if (!window.testRunner || !window.internals) {
         setTimeout(repaintTest, 500);
@@ skipping 33 matching lines @@
         testRunner.displayAsyncThen(continueRepaintTest);
     };
 }
 
 function runRepaintAndPixelTest()
 {
     window.enablePixelTesting = true;
     runRepaintTest();
 }
 
+function runAfterDisplay(callback)
+{
+    if (!window.testRunner) {
+        setTimeout(callback, 500);
+    } else {
+        testRunner.waitUntilDone();
+        testRunner.displayAsyncThen(callback);
+    }
+}
+
 function forceStyleRecalc()
 {
     if (document.body)
         document.body.offsetTop;
     else if (document.documentElement)
         document.documentElement.offsetTop;
 }
 
 function finishRepaintTest()
 {
@@ skipping 117 matching lines @@
             } else {
                 var newRect = [xBegin, y, xWidth, 1];
                 nextRectsMayContinue.push(newRect);
                 result.push(newRect);
             }
         }
         rectsMayContinue = nextRectsMayContinue;
     }
     return result;
 }