Add a DCHECK to ECSignatureCreator::SetFactoryForTesting to help avoid use-after-free problems.

Review URL: https://chromiumcodereview.appspot.com/10828118

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@149506 0039d316-1c4b-4281-b951-d872f2087c98

crypto/ec_signature_creator.cc

@@ -4,6 +4,7 @@
 
 #include "crypto/ec_signature_creator.h"
 
+#include "base/logging.h"
 #include "crypto/ec_signature_creator_impl.h"
 
 namespace crypto {
@@ -24,6 +25,9 @@ ECSignatureCreator* ECSignatureCreator::Create(ECPrivateKey* key) {
 // static
 void ECSignatureCreator::SetFactoryForTesting(
     ECSignatureCreatorFactory* factory) {
+  // We should always clear the factory after each test to avoid
+  // use-after-free problems.
+  DCHECK(!g_factory_ || !factory);
   g_factory_ = factory;
 }