Allow media track switching.

content/renderer/media/media_interface_provider.cc

Index: content/renderer/media/media_interface_provider.cc
diff --git a/content/renderer/media/media_interface_provider.cc b/content/renderer/media/media_interface_provider.cc
index 8f779f5bf39dddd7a374c9949ee9788350077769..b542c6c543780eb4f7c02612e48f8babde46f4ae 100644
--- a/content/renderer/media/media_interface_provider.cc
+++ b/content/renderer/media/media_interface_provider.cc
@@ -16,7 +16,9 @@ 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());
@@ -25,6 +27,13 @@ MediaInterfaceProvider::~MediaInterfaceProvider() {
 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_) {