Clean-up BrowserMessageFilter::Send.

Wrap the message in a unique_ptr to make sure it isn't leaked, if some
branch doesn't pass it on to another sender or delete it.
Also change a conditional NOTREACHED to a DCHECK following the style
guide[1].


[1] chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md#check_dcheck_and-notreached

Change-Id: I149d2b28d462be32b7170c0b8973fe74ad74ed6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2507277Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Tal Pressman <talp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822558}

content/public/browser/browser_message_filter.cc

@@ -140,27 +140,26 @@ void BrowserMessageFilter::OnDestruct() const {
 }
 
 bool BrowserMessageFilter::Send(IPC::Message* message) {
-  if (message->is_sync()) {
+  std::unique_ptr<IPC::Message> msg(message);
+
   // We don't support sending synchronous messages from the browser.  If we
   // really needed it, we can make this class derive from SyncMessageFilter
   // but it seems better to not allow sending synchronous messages from the
   // browser, since it might allow a corrupt/malicious renderer to hang us.
-    NOTREACHED() << "Can't send sync message through BrowserMessageFilter!";
-    return false;
-  }
+  DCHECK(!msg->is_sync())
+    << "Can't send sync message through BrowserMessageFilter!";
 
   if (!BrowserThread::CurrentlyOn(BrowserThread::IO)) {
     GetIOThreadTaskRunner({})->PostTask(
         FROM_HERE,
         base::BindOnce(base::IgnoreResult(&BrowserMessageFilter::Send), this,
-                       message));
+                       msg.release()));
     return true;
   }
 
   if (sender_)
-    return sender_->Send(message);
+    return sender_->Send(msg.release());
 
-  delete message;
   return false;
 }