PPAPI: Fix raymes's review comments I missed

content/renderer/pepper/message_channel.cc

Index: content/renderer/pepper/message_channel.cc
diff --git a/content/renderer/pepper/message_channel.cc b/content/renderer/pepper/message_channel.cc
index df56988af09c8de1b2882f0e17abd4d835d72c1c..2ce6009fcc4370d29723c12e2117c33b8644f1b5 100644
--- a/content/renderer/pepper/message_channel.cc
+++ b/content/renderer/pepper/message_channel.cc
@@ -166,9 +166,9 @@ void MessageChannel::Start() {
   if (dispatcher)
     dispatcher->AddSyncMessageStatusObserver(this);
 
-  // We can't drain the JS message queue directly
-  // since we haven't finished initializing the PepperWebPluginImpl yet, so
-  // the plugin isn't available in the DOM.
+  // We can't drain the JS message queue directly since we haven't finished
+  // initializing the PepperWebPluginImpl yet, so the plugin isn't available in
+  // the DOM.
   DrainJSMessageQueueSoon();
 
   plugin_message_queue_state_ = SEND_DIRECTLY;
@@ -209,6 +209,7 @@ void MessageChannel::BeginBlockOnSyncMessage() {
 }
 
 void MessageChannel::EndBlockOnSyncMessage() {
+  DCHECK_GT(blocking_message_depth_, 0);
   --blocking_message_depth_;
   if (!blocking_message_depth_)
     DrainJSMessageQueueSoon();