Fix a bug where packing an extension with bad private key causes crash.

chrome/browser/extensions/extension_creator.cc

Index: chrome/browser/extensions/extension_creator.cc
diff --git a/chrome/browser/extensions/extension_creator.cc b/chrome/browser/extensions/extension_creator.cc
index e344338297db7fc9c296e8a330f87a982b85ce45..da9b6a5c650d489cc2eab8de658bada14001ec87 100644
--- a/chrome/browser/extensions/extension_creator.cc
+++ b/chrome/browser/extensions/extension_creator.cc
@@ -228,7 +228,11 @@ bool ExtensionCreator::SignZip(const base::FilePath& zip_path,
   }
   zip_handle.Close();
 
-  signature_creator->Final(signature);
+  if (!signature_creator->Final(signature)) {
+    error_message_ =
+        l10n_util::GetStringUTF8(IDS_EXTENSION_PRIVATE_KEY_INVALID);
+    return false;
+  }
   return true;
 }