Add EventHandlerRegistry

LayoutTests/fast/events/scroll-event-handler-count.html

+<script src="../../resources/js-test.js"></script>
+<script>
+description("This test checks that we correctly update the scroll event handler count as event handlers are added and removed");

[Rick Byers, 2014/03/27 16:43:31]

Note that I've added a bunch more testing to touch-event-handler-count.html from
what was in the (apparently copied/pasted) wheel-event version.  Now that the
code is all unified, it seems silly to have 3 tests which are mostly (but not
completely copy/paste of each other).  Perhaps it's worth unifying into a single
test that uses a mix of event types (verifying each type and each scenario but
not every possible combination of type+scenario)?

[Sami, 2014/04/02 19:58:05]

Yes, definitely. No need to duplicate the same test three times over. I've now
got a single event-handler-count.html that covers all the scenarios with
variable event types.

+
+(function() {
+    // Test addEventListener/removeEventListener on the document.
+    var listener = function() { }
+
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+    document.addEventListener('scroll', listener, true);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+    document.addEventListener('scroll', listener, false);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '2');
+    document.removeEventListener('scroll', listener, true);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+
+    // Try removing the capturing listener again.
+    document.removeEventListener('scroll', listener, true);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+
+    document.removeEventListener('scroll', listener, false);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+})();
+
+(function() {
+    // Test setting onscroll on the document.
+
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+    document.onscroll = function() { }
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+    document.onscroll = function() { }
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+    document.onscroll = null;
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+})();
+
+(function() {
+    // Test addEventListener/removeEventListener on the window.
+    var listener = function() { }
+
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+    window.addEventListener('scroll', listener, true);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+    window.addEventListener('scroll', listener, false);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '2');
+    window.removeEventListener('scroll', listener, true);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+
+    // Try removing the capturing listener again.
+    window.removeEventListener('scroll', listener, true);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+
+    window.removeEventListener('scroll', listener, false);
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+})();
+
+(function() {
+    // Test setting onscroll on the window.
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+    window.onscroll = function() { }
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+    window.onscroll = function() { }
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '1');
+    window.onscroll = null;
+    shouldBe('window.internals.scrollEventHandlerCount(document)', '0');
+})();
+
+</script>
+</body>