Fix ThreadSafeAssociatedInterfacePtrProvider raciness.

content/renderer/mojo/thread_safe_associated_interface_ptr_provider.h

Index: content/renderer/mojo/thread_safe_associated_interface_ptr_provider.h
diff --git a/content/renderer/mojo/thread_safe_associated_interface_ptr_provider.h b/content/renderer/mojo/thread_safe_associated_interface_ptr_provider.h
index a05f2b9ffe16755d7b23bd9f16456ea043896f46..87dd2ab304fd9a03d6bb2942b94997389d05b268 100644
--- a/content/renderer/mojo/thread_safe_associated_interface_ptr_provider.h
+++ b/content/renderer/mojo/thread_safe_associated_interface_ptr_provider.h
@@ -29,7 +29,8 @@ class ThreadSafeAssociatedInterfacePtrProvider {
   scoped_refptr<mojo::ThreadSafeAssociatedInterfacePtr<Interface>>
   CreateInterfacePtr() {
     scoped_refptr<mojo::ThreadSafeAssociatedInterfacePtr<Interface>> ptr =
-        mojo::ThreadSafeAssociatedInterfacePtr<Interface>::CreateUnbound();
+        mojo::ThreadSafeAssociatedInterfacePtr<Interface>::CreateUnbound(
+            channel_proxy_->ipc_task_runner());
     channel_proxy_->RetrieveAssociatedInterfaceOnIOThread<Interface>(base::Bind(

[leonhsl(Using Gerrit), 2016/12/30 06:53:15]

I'm not sure I fully understand,, would you please help to clarify this
question? Thanks.
With changes of thread_safe_interface_ptr.h in this CL, here I suppose
ChannelProxy::RetrieveAssociatedInterfaceOnIOThread() is required to post a task
A to ipc task runner, and task A MUST call
ThreadSafeAssociatedInterfacePtrProvider::BindInterfacePtr() *directly* there,
and such scenario is not allowed? : "Task A posts to the same ipc task runner
another task B to call BindInterfacePtr()."

[Jay Civelli, 2017/01/03 16:40:56]

I am not sure I fully understand the question.
The IPC task runner runs on the IO thread, so posting the bind to the IPC task
runner guarantees any calls made on the ThreadSafeAssociatedInterfacePtr (once
it has been returned) will be posted to the same task runner and will happen
after the bind, on the IO thread.

[leonhsl(Using Gerrit), 2017/01/04 03:35:03]

So I suppose the following scenario maybe is not allowed.
After CreateUnbound returned, post a task A to the ipc task runner, but task A
does not execute BindInterfacePtr directly, instead it posts task B to the same
ipc task runner to execute BindInterfacePtr. In such case the returned
ThreadSafeAssociatedInterfacePtr from CreateUnbound() still can not be used to
make any calls at once, is my understanding correct? If so I think it'd better
add some explicit comments about this restriction around CreateUnbound().

         &ThreadSafeAssociatedInterfacePtrProvider::BindInterfacePtr<Interface>,
         ptr));