Use the Mojo StubBindings interface correctly in WebUSB LayoutTests.

mojo/public/js/connection.js

Index: mojo/public/js/connection.js
diff --git a/mojo/public/js/connection.js b/mojo/public/js/connection.js
index 62e8798fb2d736fea2d68e075aba818ff6df92ca..5e636fb997e5cdf3e27b78a96db79e05ecb01a68 100644
--- a/mojo/public/js/connection.js
+++ b/mojo/public/js/connection.js
@@ -25,6 +25,10 @@ define("mojo/public/js/connection", [
     this.remote = remoteProxy;
 
     this.router_.setIncomingReceiver(localStub);
+    this.router_.setErrorHandler(() => {
+      if (this.local && StubBindings(this.local).connectionErrorHandler)
+        StubBindings(this.local).connectionErrorHandler();
+    });
     if (this.remote)
       this.remote.receiver_ = router;