Support exposing Mojo services between render frames, render threads, and their respective hosts.

chrome/browser/ui/webui/mojo_web_ui_controller.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/mojo_web_ui_controller.h"
 
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/webui/mojo_web_ui_handler.h"
+#include "content/public/browser/render_frame_host.h"
+#include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_ui_data_source.h"
 #include "content/public/common/bindings_policy.h"
+#include "content/public/common/service_registry.h"
 #include "mojo/public/cpp/system/core.h"
 
 MojoWebUIController::MojoWebUIController(content::WebUI* contents)
-    : WebUIController(contents),
-      mojo_data_source_(NULL) {
+    : WebUIController(contents), mojo_data_source_(NULL), weak_factory_(this) {
 }
 
 MojoWebUIController::~MojoWebUIController() {
 }
 
 void MojoWebUIController::RenderViewCreated(
     content::RenderViewHost* render_view_host) {
   render_view_host->AllowBindings(content::BINDINGS_POLICY_WEB_UI);
-
-  mojo::MessagePipe pipe;
-  ui_handler_ = CreateUIHandler(pipe.handle0.Pass());
-  render_view_host->SetWebUIHandle(pipe.handle1.Pass());
+  render_view_host->GetProcess()->ActivateMojo();

[darin (slow to review), 2014/06/18 00:09:28]

I don't think we want to call ActivateMojo() here. This should really happen
more transparently as there could be a variety of services that would otherwise
need to call ActivateMojo(). Maybe we can do this from GetServiceRegistry()?

[Sam McNally, 2014/06/18 01:31:40]

Done.

+  render_view_host->GetMainFrame()->GetServiceRegistry()->AddService(
+      "webui_controller",
+      base::Bind(&MojoWebUIController::CreateAndStoreUIHandler,
+                 weak_factory_.GetWeakPtr()));
 }
 
 void MojoWebUIController::AddMojoResourcePath(const std::string& path,
                                               int resource_id) {
   if (!mojo_data_source_) {
     mojo_data_source_ = content::WebUIDataSource::AddMojoDataSource(
         Profile::FromWebUI(web_ui()));
   }
   mojo_data_source_->AddResourcePath(path, resource_id);
 }
+
+void MojoWebUIController::CreateAndStoreUIHandler(
+    mojo::ScopedMessagePipeHandle handle) {
+  ui_handler_ = CreateUIHandler(handle.Pass());
+}