fix(dialog): correctly disable keydown listener for escapeToClose

Currently there was a duplicated variable `target`, which got replaced later and the `target` variable became the actual `element` not the `parent` anymore.

Fixes #7214 Fixes #5153

  Closes #7222

src/components/dialog/dialog.js

@@ -732,7 +732,7 @@ function MdDialogProvider($$interimElementProvider) {
       };
 
       if (options.escapeToClose) {
-        var target = options.parent;
+        var parentTarget = options.parent;
         var keyHandlerFn = function(ev) {
           if (ev.keyCode === $mdConstant.KEY_CODE.ESCAPE) {
             ev.stopPropagation();
@@ -744,13 +744,13 @@ function MdDialogProvider($$interimElementProvider) {
 
         // Add keydown listeners
         element.on('keydown', keyHandlerFn);
-        target.on('keydown', keyHandlerFn);
+        parentTarget.on('keydown', keyHandlerFn);
 
         // Queue remove listeners function
         removeListeners.push(function() {
 
           element.off('keydown', keyHandlerFn);
-          target.off('keydown', keyHandlerFn);
+          parentTarget.off('keydown', keyHandlerFn);
 
         });
       }