Refactor Blink's ServiceConnector and add ability to mock in layout tests

third_party/WebKit/LayoutTests/resources/mojo-helpers.js

Index: third_party/WebKit/LayoutTests/resources/mojo-helpers.js
diff --git a/third_party/WebKit/LayoutTests/resources/mojo-helpers.js b/third_party/WebKit/LayoutTests/resources/mojo-helpers.js
index 92ddd8d5ae3e7c07dbd8dcf2bdcbf9ab341a1a46..95c1c60fcdc871b7a115df67d486aaaeb65840e7 100644
--- a/third_party/WebKit/LayoutTests/resources/mojo-helpers.js
+++ b/third_party/WebKit/LayoutTests/resources/mojo-helpers.js
@@ -27,34 +27,40 @@ let define = (function(){
   }
 })();
 
-define('Mojo Helpers', [
-    'mojo/public/js/core',
-    'mojo/public/js/router',
-    'mojo/public/js/support',
-    'content/public/renderer/frame_interfaces',
-    'content/public/renderer/interfaces',
-    'content/shell/renderer/layout_test/frame_interface_registry',
-    'content/shell/renderer/layout_test/interface_registry',
-], (core, router, support, frameInterfaces, interfaces, frameInterfaceRegistry,
-    interfaceRegistry) => {
-  let tearDown = () => {
-    frameInterfaces.clearInterfaceOverridesForTesting();
-    interfaces.clearInterfaceOverridesForTesting();
-  };
-  addEventListener('unload', tearDown);
-  if (window.add_completion_callback)
-    add_completion_callback(tearDown);
+define(
+    'Mojo Helpers',
+    [
+      'mojo/public/js/core',
+      'mojo/public/js/router',
+      'mojo/public/js/support',
+      'content/public/renderer/connector',
+      'content/public/renderer/frame_interfaces',
+      'content/public/renderer/interfaces',
+      'content/shell/renderer/layout_test/frame_interface_registry',
+      'content/shell/renderer/layout_test/interface_registry',
+    ],
+    (core, router, support, connector, frameInterfaces, interfaces,
+     frameInterfaceRegistry, interfaceRegistry) => {
+      let tearDown = () => {
+        connector.clearInterfaceOverridesForTesting();

[dcheng, 2017/03/21 18:56:18]

Do we have any documentation about the differences between these three things?
If I wanted to write a layout test and mock out interfaces, which one of these
things should I be mocking interfaces against?

I guess connector is to let us mock interfaces for things that Blink connects
*to*, while frameInterfaces / interfaces are for mocking interfaces that Blink
implements itself? Do I have this roughly correct? =)

[Ken Rockot(use gerrit already), 2017/03/23 04:56:04]

No, they're all different ways for the client (blink) to connect *to* things,
each with their own API for locally intercepting those outgoing connections and
routing them back to fake local impls. e.g. you have a web API with a C++ impl
that talks to some mojom interface normally implemented in the browser, and
within a layout test you can intercept its requests and route them instead to a
JS mock impl of the target interface.

interfaces is the original thing - we didn't have services way back then, just a
big open interface registry in the RPH, and this is an interface provider which
routes interface requests to that with no additional context. This is
essentially deprecated but still in use (of course). We'll delete it soon.

frameInterfaces is similarly an interface provider, but scoped to an RFH. I
expect that this will stick around in some form, as we still have no better way
of arranging for some frame hosting/navigation service to broker interface
requests on a frame's behalf.

connector is the generic service manager connector API that services should
generally use to connect to each other. It binds requests in the form of
(target_service, interface_request), brokered through the service manager. There
is no reason why existing uses of the RPH interface registry cannot be trivially
ported to uses of connector which bind to ("content_browser",
whatever_interface), for example, which is how we plan to get rid of the first
thing.

+        frameInterfaces.clearInterfaceOverridesForTesting();
+        interfaces.clearInterfaceOverridesForTesting();
+      };
+      addEventListener('unload', tearDown);
+      if (window.add_completion_callback)
+        add_completion_callback(tearDown);
 
-  return {
-    core,
-    router,
-    support,
-    frameInterfaces,
-    frameInterfaceRegistry,
-    interfaces,
-    interfaceRegistry,
-  };
-});
+      return {
+          core,
+          router,
+          support,
+          connector,
+          frameInterfaces,
+          frameInterfaceRegistry,
+          interfaces,
+          interfaceRegistry,
+      };
+    });
 
 // Returns a promise to an object that exposes common Mojo module interfaces.
 // Additional modules to load can be specified in the |modules| parameter. The