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

third_party/WebKit/LayoutTests/editing/spelling/resources/util.js

 function log(msg)
 {
     document.getElementById("console").innerHTML += (msg + "\n");
 }
 
 function verifySpellTest(nretry, opt_doNotFinishTest)
 {
     var node = window.destination;
     if (window.destination.childNodes.length > 0)
         node = window.destination.childNodes[0];
     if (nretry && !internals.markerCountForNode(node, "spelling")) {
         window.setTimeout(function() { verifySpellTest(nretry - 1, opt_doNotFinishTest); }, 0);
         return;
     }
     testFunctionCallback(node);
     if (!opt_doNotFinishTest)
         finishJSTest();
 }
 
 function initSpellTest(testElementId, testText, testFunction, opt_doNotFinishTest)
 {
     if (!window.internals || !window.testRunner) {
         log("FAIL Incomplete test environment");
         return;
     }
+    testRunner.setMockSpellCheckerEnabled(true);
     testFunctionCallback = testFunction;
     jsTestIsAsync = true;
     internals.settings.setSmartInsertDeleteEnabled(true);
     internals.settings.setSelectTrailingWhitespaceEnabled(false);
     internals.settings.setEditingBehavior("win");
     window.destination = document.getElementById(testElementId);
     window.destination.focus();
     document.execCommand("InsertText", false, testText);
     window.setTimeout(function() { verifySpellTest(10, opt_doNotFinishTest); }, 0);
 }
@@ skipping 42 matching lines @@
     step();
     step_timeout(() => {
         test.step(() => assertion());
         runNextStep(test, steps, assertions);
     }, 50);
 }
 
 function runSpellingTest(steps, assertions, opt_title)
 {
     var t = async_test(opt_title);
-    if (!window.internals) {
-        t.step(() => assert_unreached('internals is required for this test'));
+    if (!window.internals || !window.testRunner) {
+        t.step(() => assert_unreached('Incomplete test environment'));
         t.done();
         return;
     }
 
+    testRunner.setMockSpellCheckerEnabled(true);
     runNextStep(t, steps, assertions);
 }