Fix crashes loading internal chrome pages powered by Mojo

chrome/browser/chrome_content_browser_manifest_overlay.json

 {
   "name": "service:content_browser",
   "display_name": "Chrome",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "renderer": [
           "autofill::mojom::AutofillDriver",
           "autofill::mojom::PasswordManagerDriver",
           "extensions::StashService",
@@ skipping 30 matching lines @@
           "autofill::mojom::AutofillDriver",
           "autofill::mojom::PasswordManagerDriver",
           "blink::mojom::ShareService",
           "dom_distiller::mojom::DistillabilityService",
           "dom_distiller::mojom::DistillerJavaScriptService",
           "extensions::KeepAlive",
           "extensions::mime_handler::MimeHandlerService",
           "media_router::mojom::MediaRouter",
           "mojom::OmniboxPageHandler",
           "password_manager::mojom::CredentialManager",
-          "translate::mojom::ContentTranslateDriver"
+          "translate::mojom::ContentTranslateDriver",
+
+          // TODO(beng): These should be moved to a separate capability.

[Tom Sepez, 2016/10/31 21:45:05]

nit: Strictly speaking, Comments aren't allowed in JSON :(.  See www.json.org.

+          "mojom::OmniboxPageHandler",

[Will Harris, 2016/10/31 21:54:08]

how do we know that we have all the interfaces listed and none are missing?

+          "mojom::PluginsPageHandler",
+          "mojom::SiteEngagementUIHandler",
+          "mojom::UsbInternalsPageHandler"
         ]
       }
     }
   }
 }