Revert "Don't force layout for mouse event hit tests"

LayoutTests/fast/files/resources/setup-for-read-common.js

 function log(message)
 {
     document.getElementById('console').appendChild(document.createTextNode(message + "\n"));
     if (message == "DONE") {
         if (window && window.testRunner)
             testRunner.notifyDone();
     }
 }
 
 function onInputFileChange(testFileInfoList)
 {
     var files = document.getElementById("file").files;
     var testFiles = { };
     for (var i = 0; i < files.length; i++)
         testFiles[testFileInfoList[i]['name']] = files[i];
 
     startTest(testFiles);
 }
 
 function runTests(testFileInfoList)
 {
     var pathsOnly = testFileInfoList.map(function(fileSpec) { return fileSpec['path']; });
-    // Mouse events only work after an initial layout
-    document.body.offsetLeft;
     eventSender.beginDragWithFiles(pathsOnly);
     eventSender.mouseMoveTo(10, 10);
     eventSender.mouseUp();
 }
 
 function startWorker(testFiles, workerScriptURL)
 {
     var worker = new Worker(workerScriptURL);
     worker.onmessage = function(event)
     {
         log(event.data);
         if (event.data == "DONE") {
             if (window.testRunner)
                 testRunner.notifyDone();
         }
     }
     worker.onerror = function(event)
     {
         log("Received error from worker: " + event.message);
         if (window.testRunner)
             testRunner.notifyDone();
     }
     worker.postMessage(testFiles);
 }