[cssom-view] Escape Promise<undefined> properly.

Closes #12930

Author: emilio

cssom-view-1/Overview.bs

@@ -590,12 +590,12 @@ partial interface Window {
     [Replaceable] readonly attribute double pageXOffset;
     [Replaceable] readonly attribute double scrollY;
     [Replaceable] readonly attribute double pageYOffset;
-    Promise<undefined> scroll(optional ScrollToOptions options = {});
-    Promise<undefined> scroll(unrestricted double x, unrestricted double y);
-    Promise<undefined> scrollTo(optional ScrollToOptions options = {});
-    Promise<undefined> scrollTo(unrestricted double x, unrestricted double y);
-    Promise<undefined> scrollBy(optional ScrollToOptions options = {});
-    Promise<undefined> scrollBy(unrestricted double x, unrestricted double y);
+    Promise&lt;undefined> scroll(optional ScrollToOptions options = {});
+    Promise&lt;undefined> scroll(unrestricted double x, unrestricted double y);
+    Promise&lt;undefined> scrollTo(optional ScrollToOptions options = {});
+    Promise&lt;undefined> scrollTo(unrestricted double x, unrestricted double y);
+    Promise&lt;undefined> scrollBy(optional ScrollToOptions options = {});
+    Promise&lt;undefined> scrollBy(unrestricted double x, unrestricted double y);
 
     // client
     [Replaceable] readonly attribute long screenX;
@@ -1320,13 +1320,13 @@ partial interface Element {
 
   boolean checkVisibility(optional CheckVisibilityOptions options = {});
 
-  Promise<undefined> scrollIntoView(optional (boolean or ScrollIntoViewOptions) arg = {});
-  Promise<undefined> scroll(optional ScrollToOptions options = {});
-  Promise<undefined> scroll(unrestricted double x, unrestricted double y);
-  Promise<undefined> scrollTo(optional ScrollToOptions options = {});
-  Promise<undefined> scrollTo(unrestricted double x, unrestricted double y);
-  Promise<undefined> scrollBy(optional ScrollToOptions options = {});
-  Promise<undefined> scrollBy(unrestricted double x, unrestricted double y);
+  Promise&lt;undefined> scrollIntoView(optional (boolean or ScrollIntoViewOptions) arg = {});
+  Promise&lt;undefined> scroll(optional ScrollToOptions options = {});
+  Promise&lt;undefined> scroll(unrestricted double x, unrestricted double y);
+  Promise&lt;undefined> scrollTo(optional ScrollToOptions options = {});
+  Promise&lt;undefined> scrollTo(unrestricted double x, unrestricted double y);
+  Promise&lt;undefined> scrollBy(optional ScrollToOptions options = {});
+  Promise&lt;undefined> scrollBy(unrestricted double x, unrestricted double y);
   attribute unrestricted double scrollTop;
   attribute unrestricted double scrollLeft;
   readonly attribute long scrollWidth;