Move in-GPU mojo:media app to new thread

content/public/common/mojo_application_info.h

Index: content/public/common/mojo_application_info.h
diff --git a/content/public/common/mojo_application_info.h b/content/public/common/mojo_application_info.h
index 72513bdfd8362aeaf6e1ac6121b974a1ab8eacc8..b5bcc4477c6ad6d8a79b4e86e96151a320924938 100644
--- a/content/public/common/mojo_application_info.h
+++ b/content/public/common/mojo_application_info.h
@@ -18,6 +18,8 @@ class SingleThreadTaskRunner;
 
 namespace content {
 
+// MojoApplicationInfo provides details necessary to construct and bind new
+// instances of embedded Mojo applications.
 struct CONTENT_EXPORT MojoApplicationInfo {
   using ApplicationFactory = base::Callback<std::unique_ptr<shell::ShellClient>(
       const base::Closure& quit_closure)>;
@@ -26,8 +28,21 @@ struct CONTENT_EXPORT MojoApplicationInfo {
   MojoApplicationInfo(const MojoApplicationInfo& other);
   ~MojoApplicationInfo();
 
+  // A factory function which will be called to produce a new ShellClient
+  // instance for this app whenever one is needed.
   ApplicationFactory application_factory;
+
+  // The task runner on which to construct and bind new ShellClient instances
+  // for this app. If null, behavior depends on the value of |use_own_thread|
+  // below.
   scoped_refptr<base::SingleThreadTaskRunner> application_task_runner;
+
+  // If |application_task_runner| is null, setting this to |true| will give
+  // each instance of this app its own thread to run on. Setting this to |false|
+  // (the default) will instead run the app on the main thread's task runner.
+  //
+  // If |application_task_runner| is not null, this value is ignored.
+  bool use_own_thread = false;

[Ken Rockot(use gerrit already), 2016/05/13 20:19:03]

Note for review: I considered changing null application_task_runner to mean "use
your own thread" and require the main thread case to pass an explicit task
runner. That would avoid the need for this flag.

I chose to use an explicit opt-in flag instead, because I didn't want it to be
so easy for embedded apps to spawn new threads without realizing it.

 };
 
 }  // namespace content