Avoid adding placeholder when deleting last text in root

LayoutTests/fast/events/script-tests/event-input-contentEditable.js

 description("This tests that the input events are dispatched when contentEditable nodes are edited");
 
 var actualInputEventCount = 0;
 var expectedInputEventCount = 0;
 
 function fired(evt, expectedId, expectedText)
 {
     actualInputEventCount++;
     shouldBe("event.target.id", "'" + expectedId + "'");
     shouldBe("event.target.innerHTML", "'" + expectedText + "'");
@@ skipping 33 matching lines @@
 var target1 = makeTestTarget('<p id="target1" contentEditable>Text should be insert via script:</p>');
 target1.addEventListener("input", function(evt) { testFailed("should not be reached"); });
 target1.firstChild.data += "Text";
 
 // An event should be dispatched even if resulting DOM tree doesn't change after the edit. (with replacing it)
 var target2Text = "This text should not be changed.";
 var target2 = setupForFiringTest('<p id="target2" contentEditable>This text should not be changed.</p>', target2Text);
 document.execCommand("insertText", false, target2Text);
 
 // An "delete" command should dispatch an input event.
-var target3 = setupForFiringTest('<p id="target3" contentEditable>This text shouldn be deleted.</p>', "<br>");
+var target3 = setupForFiringTest('<p id="target3" contentEditable>This text shouldn be deleted.</p>', '');
 document.execCommand("delete", false);
 
 // A command other than text-editing should dispatch an input event.
 // Also note that createLink is a composite command, 
 // so this test also ensures that even composite command dispatches the event only once.
 var target4 = setupForFiringTest('<p id="target4" contentEditable>This text should be a link.</p>', "<a href=\"http://www.example.com/\">This text should be a link.</a>");
 document.execCommand("createLink", false, "http://www.example.com/");
 
 // An event shouldn't be dispatched to a 'display:none' node.
 var target5 = makeTestTarget('<p id="target5" contentEditable>This will not be rendered.</p>');
@@ skipping 16 matching lines @@
 target6end.addEventListener("input", function(evt) { testFailed("should not be reached"); });
 target6middle.addEventListener("input", function(evt) { fired(evt, "target6end", ""); });
 sel.selectAllChildren(target6parent);
 document.execCommand("createLink", false, "http://www.example.com/");
 
 // Ensure key events can cause the event 
 var target7 = setupForFiringTest('<p id="target7" contentEditable>Replaced</p>', "X");
 sel.selectAllChildren(target7);
 eventSender.keyDown('X');
 
-var target8 = setupForFiringTest('<p id="target8" contentEditable>Deleted</p>', '<br>');
+var target8 = setupForFiringTest('<p id="target8" contentEditable>Deleted</p>', '');
 sel.selectAllChildren(target8);
 eventSender.keyDown('delete');
 
 var target9parent = makeTestTarget('<div id="target9parent" contenteditable><div id="target9child" contenteditable>foo</div></div>');
 var target9child = document.getElementById('target9child');
 target9child.addEventListener("input", function(evt) { testFailed("should not be reached"); });
 target9parent.addEventListener("input", function(evt) { fired(evt, target9parent.id, '<div id="target9child" contenteditable="">Replacing</div>'); });
 sel.selectAllChildren(target9child);
 document.execCommand("insertText", false, "Replacing");
 expectedInputEventCount++;
 
 var target10parent = makeTestTarget('<div id="t10parent" contenteditable><div id="t10child" contenteditable=false><div id="t10gch" contenteditable>foo</div></div></div>');
 var target10child = document.getElementById("t10child");
 var target10gch = document.getElementById("t10gch");
 target10gch.addEventListener("input", function(evt) { fired(evt, target10gch.id, 'Replacing'); });
 sel.selectAllChildren(target10gch);
 document.execCommand("insertText", false, "Replacing");
 expectedInputEventCount++;
 
 shouldBe("expectedInputEventCount", "actualInputEventCount");
 clearTestTarget();