Adds Mojo IDL.

third_party/WebKit/Source/core/mojo/MojoWatcher.idl

Index: third_party/WebKit/Source/core/mojo/MojoWatcher.idl
diff --git a/chrome/test/data/extensions/api_test/notifications/api/other_app/index.js b/third_party/WebKit/Source/core/mojo/MojoWatcher.idl
similarity index 67%
copy from chrome/test/data/extensions/api_test/notifications/api/other_app/index.js
copy to third_party/WebKit/Source/core/mojo/MojoWatcher.idl
index a0762c7c8098f7151687cd17c7786bb3c68f3d8e..c073555de0504f48845b7750e03be892f80da608 100644
--- a/chrome/test/data/extensions/api_test/notifications/api/other_app/index.js
+++ b/third_party/WebKit/Source/core/mojo/MojoWatcher.idl
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-onload = function() {
-  chrome.test.sendMessage('visible');
+[
+    Custom=VisitDOMWrapper,
+] interface MojoWatcher {
+    MojoResult cancel();

[esprehn, 2016/10/25 03:34:07]

This could also have a MojoHandle property?

[alokp, 2016/10/25 05:01:38]

Sure - if needed. The old bindings do not have this property.

Related question: It seems a more idiomatic way is to use "long" instead of an
object (similar to setInterval and clearInterval)? Would you recommend the watch
API like:
long watch(MojoHandle, MojoHandleSignals, MojoWatchCallback);
void cancelWatch(long);

Or the current one is fine? The reason I made MojoWatcher an object so as to
cancel the watch when MojoWatcher is garbage collected. But I am not sure why
most other watch APIs that I know of are implemented using an integral ID.

 };