Added a rudimentary DOM, to assist with event dispatch.

samples/openglui/src/openglui_canvas_tests.dart

Index: samples/openglui/src/openglui_canvas_tests.dart
===================================================================
--- samples/openglui/src/openglui_canvas_tests.dart	(revision 19252)
+++ samples/openglui/src/openglui_canvas_tests.dart	(working copy)
@@ -25,15 +25,19 @@
   if (canvasp == null) {
     log("Allocating canvas");
     canvas = new CanvasElement(width: w, height: h);
+    document.body.nodes.add(canvas);
   } else {
     log("Using parent canvas");
     canvas = canvasp;
-    // called from gl_driver.dart.
-    // This is a kludge; we need a clean way of handling events.
-    canvas.on.mouseDown.add((e) {
-      ++testnum;
-    });
   }
+  canvas.onMouseDown.listen((e) {
+    ++testnum;
+    isDirty = true;
+  });
+  canvas.onKeyDown.listen((e) {
+    ++testnum;
+    isDirty = true;
+  });
   ctx = canvas.getContext("2d");
   if (ctx == null) {
     throw "Failed to get 2D context";
@@ -736,39 +740,3 @@
   isDirty = false;
 }
 
-/*
-TODO(gram): below are the current entry points for input events for the
-native code version. We need to integrate these somehow with the WebGL
-version:
-*/
-onMotionDown(num when, num x, num y) {
-  ++testnum;
-  isDirty = true;
-  log("Marking dirty");
-}
-onMotionUp(num when, num x, num y) {}
-onMotionMove(num when, num x, num y) {}
-onMotionCancel(num when, num x, num y) {}
-onMotionOutside(num when, num x, num y) {}
-onMotionPointerDown(num when, num x, num y) {
-  ++testnum;
-  isDirty = true;
-  log("Marking dirty");
-}
-
-onMotionPointerUp(num when, num x, num y) {}
-
-onKeyDown(num when, int flags, int keycode, int metastate, int repeat) {
-  if (keycode == 32) {
-    ++testnum;
-    isDirty = true;
-    log("Marking dirty");
-  }
-}
-
-onKeyUp(num when, int flags, int keycode, int metastate, int repeat) {}
-
-onKeyMultiple(num when, int flags, int keycode, int metastate, int repeat) {
-}
-
-