Add DCHECK to mojo endpoint wrappers to ban null task runners

Bug: 1044268
Change-Id: I00f1c5f368ba5f97b0507c1b24f6396d2bb8eb57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2087192Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746724}

third_party/blink/renderer/platform/mojo/heap_mojo_receiver.h

@@ -37,11 +37,13 @@ class HeapMojoReceiver {
   }
   mojo::PendingRemote<Interface> BindNewPipeAndPassRemote(
       scoped_refptr<base::SequencedTaskRunner> task_runner) WARN_UNUSED_RESULT {
+    DCHECK(task_runner);
     return wrapper_->receiver().BindNewPipeAndPassRemote(
         std::move(task_runner));
   }
   void Bind(mojo::PendingReceiver<Interface> pending_receiver,
             scoped_refptr<base::SequencedTaskRunner> task_runner) {
+    DCHECK(task_runner);
     wrapper_->receiver().Bind(std::move(pending_receiver),
                               std::move(task_runner));
   }

third_party/blink/renderer/platform/mojo/heap_mojo_receiver_set.h

@@ -31,6 +31,7 @@ class HeapMojoReceiverSet {
   mojo::ReceiverId Add(ImplPointerType impl,
                        mojo::PendingReceiver<Interface> receiver,
                        scoped_refptr<base::SequencedTaskRunner> task_runner) {
+    DCHECK(task_runner);
     return wrapper_->receiver_set().Add(std::move(impl), std::move(receiver));
   }
   void Clear() { wrapper_->receiver_set().Clear(); }

third_party/blink/renderer/platform/mojo/heap_mojo_remote.h

@@ -38,11 +38,13 @@ class HeapMojoRemote {
   }
   mojo::PendingReceiver<Interface> BindNewPipeAndPassReceiver(
       scoped_refptr<base::SequencedTaskRunner> task_runner) WARN_UNUSED_RESULT {
+    DCHECK(task_runner);
     return wrapper_->remote().BindNewPipeAndPassReceiver(
         std::move(task_runner));
   }
   void Bind(mojo::PendingRemote<Interface> pending_remote,
             scoped_refptr<base::SequencedTaskRunner> task_runner) {
+    DCHECK(task_runner);
     wrapper_->remote().Bind(std::move(pending_remote), std::move(task_runner));
   }