Add more CHECKs to help investigate the Mojo bootstrap crash

ipc/mojo/scoped_ipc_support.cc

Index: ipc/mojo/scoped_ipc_support.cc
diff --git a/ipc/mojo/scoped_ipc_support.cc b/ipc/mojo/scoped_ipc_support.cc
index bcaa3a15cc57e3b131522c4a983d04e4f6a74852..ba496fdf2f87ead43f97b25e2a4cd4c9ca59e83d 100644
--- a/ipc/mojo/scoped_ipc_support.cc
+++ b/ipc/mojo/scoped_ipc_support.cc
@@ -85,6 +85,7 @@ class IPCSupportInitializer : public mojo::edk::ProcessDelegate {
 
 void IPCSupportInitializer::Init(
     scoped_refptr<base::TaskRunner> io_thread_task_runner) {
+  CHECK(io_thread_task_runner);
   base::AutoLock locker(lock_);
   DCHECK((init_count_ == 0 && !io_thread_task_runner_) ||
          io_thread_task_runner_ == io_thread_task_runner);