Fix remoting NM hosts to verify that incoming messages are dictionaries.

After crrev.com/295851 the PipeMessagingChannel verifies that incoming
messages are dictionaries and then passes them as base::Value to
OnMessage() and then OnMessage() implementation static_cast<> them to
base::DictionaryValue. This is fragile, and also it shouldn't be
PipeMessagingChannel's responsibility to verify format of the messages
it reads. Moved the check to OnMessage() implementations.

Review URL: https://codereview.chromium.org/615543004

Cr-Commit-Position: refs/heads/master@{#297274}

remoting/host/it2me/it2me_native_messaging_host.cc

@@ -87,6 +87,12 @@ void It2MeNativeMessagingHost::Start(const base::Closure& quit_closure) {
 void It2MeNativeMessagingHost::OnMessage(scoped_ptr<base::Value> message) {
   DCHECK(task_runner()->BelongsToCurrentThread());
 
+  if (message->GetType() != base::Value::TYPE_DICTIONARY) {
+    LOG(ERROR) << "Received a message that's not a dictionary.";
+    channel_->SendMessage(nullptr);
+    return;
+  }
+
   scoped_ptr<base::DictionaryValue> message_dict(
       static_cast<base::DictionaryValue*>(message.release()));
   scoped_ptr<base::DictionaryValue> response(new base::DictionaryValue());

remoting/host/native_messaging/pipe_messaging_channel.cc

@@ -72,12 +72,6 @@ void PipeMessagingChannel::Start(EventHandler* event_handler) {
 void PipeMessagingChannel::ProcessMessage(scoped_ptr<base::Value> message) {
   DCHECK(CalledOnValidThread());
 
-  if (message->GetType() != base::Value::TYPE_DICTIONARY) {
-    LOG(ERROR) << "Expected DictionaryValue";
-    Shutdown();
-    return;
-  }
-
   if (event_handler_)
     event_handler_->OnMessage(message.Pass());
 }

remoting/host/setup/me2me_native_messaging_host.cc

@@ -104,6 +104,12 @@ void Me2MeNativeMessagingHost::Start(
 void Me2MeNativeMessagingHost::OnMessage(scoped_ptr<base::Value> message) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  if (message->GetType() != base::Value::TYPE_DICTIONARY) {
+    LOG(ERROR) << "Received a message that's not a dictionary.";
+    channel_->SendMessage(nullptr);
+    return;
+  }
+
   scoped_ptr<base::DictionaryValue> message_dict(
       static_cast<base::DictionaryValue*>(message.release()));
   scoped_ptr<base::DictionaryValue> response(new base::DictionaryValue());