Do not dispatch change event when pressing spin button for input type=datetime

LayoutTests/fast/forms/resources/common-spinbutton-change-and-input-events.js

 var inputEventCounter = 0;
 var changeEventCounter = 0;
 var testInput;
 
 function testSpinButtonChangeAndInputEvents(inputType, initialValue, expectedValue, maximumValue)
 {
     description('Test for event dispatching by spin buttons in a type=' + inputType + ' input.');
     if (!window.eventSender) {
         debug('No eventSender');
         return;
@@ skipping 16 matching lines @@
     eventSender.mouseMoveTo(0, 0);
     shouldEvaluateTo('changeEventCounter', 0);
     shouldEvaluateTo('inputEventCounter', 0);
     testInput.focus();
 
     debug('Click the upper button');
     // Move the cursor on the upper button.
     var spinButton = getElementByPseudoId(internals.oldestShadowRoot(testInput), "-webkit-inner-spin-button");
     eventSender.mouseMoveTo(testInput.offsetLeft + spinButton.offsetLeft, testInput.offsetTop + testInput.offsetHeight / 4);
     eventSender.mouseDown();
+    debug('Triggers only input event on mouseDown');
+    shouldBeEqualToString('testInput.value', expectedValue);
+    shouldEvaluateTo('changeEventCounter', 0);
+    shouldEvaluateTo('inputEventCounter', 1);
+    debug('Triggers only change event on mouseUp');
     eventSender.mouseUp();
     shouldBeEqualToString('testInput.value', expectedValue);
     shouldEvaluateTo('changeEventCounter', 1);
     shouldEvaluateTo('inputEventCounter', 1);
 
     if (testInput.hasAttribute("max")) {
         debug('Click again, but the value is not changed.');
         eventSender.mouseDown();
         eventSender.mouseUp();
         shouldBeEqualToString('testInput.value', expectedValue);
         shouldEvaluateTo('changeEventCounter', 1);
         shouldEvaluateTo('inputEventCounter', 1);
     }
 
     debug('Focus on another field');
     anotherInput.focus();
     shouldEvaluateTo('changeEventCounter', 1);
     shouldEvaluateTo('inputEventCounter', 1);
 
     parent.innerHTML = '';
 }