Add a switch to TestRunner to enable/disable mock spell checker

third_party/WebKit/LayoutTests/editing/spelling/script-tests/spelling-backspace-between-lines.js

 description('Spelling markers should remain while merging two lines.');
 
 jsTestIsAsync = true;
+if (window.testRunner)
+    testRunner.setMockSpellCheckerEnabled(true);
 
 var testRoot = document.createElement("div");
 document.body.insertBefore(testRoot, document.body.firstChild);
 
 function setup(targetName)
 {
     var div = document.createElement("div");
     div.id = targetName;
     div.contentEditable = true;
     div.innerHTML = "<div>OK</div><div>OK zz OK</div>";
@@ skipping 71 matching lines @@
         return setTimeout(next, 0);
 
     if (window.internals)
         testRoot.style.display = "none";
 
     finishJSTest();
 }
 done();
 
 var successfullyParsed = true;