Allow media track switching.

content/renderer/media/media_interface_provider.cc

 // Copyright 2016 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 "content/renderer/media/media_interface_provider.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "media/mojo/interfaces/content_decryption_module.mojom.h"
 #include "media/mojo/interfaces/renderer.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "services/service_manager/public/cpp/interface_provider.h"
 
 namespace content {
 
 MediaInterfaceProvider::MediaInterfaceProvider(
     service_manager::InterfaceProvider* remote_interfaces)
-    : remote_interfaces_(remote_interfaces) {}
+    : remote_interfaces_(remote_interfaces), weak_factory_(this) {
+  task_runner_ = base::ThreadTaskRunnerHandle::Get();
+}
 
 MediaInterfaceProvider::~MediaInterfaceProvider() {
   DCHECK(thread_checker_.CalledOnValidThread());
 }
 
 void MediaInterfaceProvider::GetInterface(const std::string& interface_name,
                                           mojo::ScopedMessagePipeHandle pipe) {
   DVLOG(1) << __func__;
+  if (!task_runner_->BelongsToCurrentThread()) {
+    task_runner_->PostTask(
+        FROM_HERE, base::Bind(&MediaInterfaceProvider::GetInterface,
+                              weak_factory_.GetWeakPtr(), interface_name,

[DaleCurtis, 2017/03/24 19:35:22]

Can't vend WeakPtrs from a different thread like this; it's not thread safe. You
at least need to bind and keep alive one WeakPtr on |task_runner_|.

[servolk, 2017/03/24 21:15:32]

Done (although I'm a little surprised. shouldn't there be a dcheck about this if
it's unsafe? i.e. shouldn't we have a dcheck(same thread as weak factory ctor)
inside the GetWeakPtr to prevent unsafe usage?).

[DaleCurtis, 2017/03/24 21:30:38]

Hard to DCHECK since it's a raciness issue.

+                              base::Passed(&pipe)));
+    return;
+  }
   DCHECK(thread_checker_.CalledOnValidThread());
 
   if (interface_name == media::mojom::ContentDecryptionModule::Name_) {
     GetMediaInterfaceFactory()->CreateCdm(
         mojo::MakeRequest<media::mojom::ContentDecryptionModule>(
             std::move(pipe)));
   } else if (interface_name == media::mojom::Renderer::Name_) {
     GetMediaInterfaceFactory()->CreateRenderer(
         std::string(),
         mojo::MakeRequest<media::mojom::Renderer>(std::move(pipe)));
@@ skipping 23 matching lines @@
 }
 
 void MediaInterfaceProvider::OnConnectionError() {
   DVLOG(1) << __func__;
   DCHECK(thread_checker_.CalledOnValidThread());
 
   media_interface_factory_.reset();
 }
 
 }  // namespace content