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..54681907496b430e1737d78471e03f292e7aebeb 100644
--- a/content/renderer/media/media_interface_provider.cc
+++ b/content/renderer/media/media_interface_provider.cc
@@ -16,7 +16,10 @@ 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();
+  weak_this_ = weak_factory_.GetWeakPtr();
+}
 
 MediaInterfaceProvider::~MediaInterfaceProvider() {
   DCHECK(thread_checker_.CalledOnValidThread());
@@ -25,6 +28,13 @@ 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_this_,
+                              interface_name, base::Passed(&pipe)));
+    return;
+  }
+
   DCHECK(thread_checker_.CalledOnValidThread());
 
   if (interface_name == media::mojom::ContentDecryptionModule::Name_) {