Avoid incrementing an invalid iterator in the utility process client.

chrome/utility/chrome_content_utility_client.cc

Index: chrome/utility/chrome_content_utility_client.cc
diff --git a/chrome/utility/chrome_content_utility_client.cc b/chrome/utility/chrome_content_utility_client.cc
index 8bd49b41ab339f9c7cc56db93da6ead3a4bcff82..962090ed31fada1360e247794d1534eff5776d4a 100644
--- a/chrome/utility/chrome_content_utility_client.cc
+++ b/chrome/utility/chrome_content_utility_client.cc
@@ -178,6 +178,15 @@ bool ChromeContentUtilityClient::OnMessageReceived(
   for (Handlers::iterator it = handlers_.begin();

[jochen (gone - plz use gerrit), 2016/05/06 10:32:30]

why not:

if (handled) return true;

for (auto& handler : handlers_)
  if (handler->OnMessageReceived(message)) return true;

return false;

[Anand Mistry (off Chromium), 2016/05/09 02:32:14]

I was just trying to minimise the change. I've changed the logic, but kept the
comment (mostly).

        !handled && it != handlers_.end(); ++it) {
     handled = (*it)->OnMessageReceived(message);
+
+    // Warning, this is a hack! At least one of the utility process handlers
+    // adds a new handler to |handlers_| when it handles a message. This causes
+    // |it| to become invalid and hence the increment, which happens before
+    // checking the loop condition, is an invalid operation. For now, just
+    // early-out of this loop and avoid incrementing the iterator. Eventually,
+    // this will be fixed by moving everything to Mojo.
+    if (handled)
+      return true;
   }
 
   return handled;