Cut down on usage of deprecated APIs in //crypto.

net/spdy/spdy_test_util_common.cc

Index: net/spdy/spdy_test_util_common.cc
diff --git a/net/spdy/spdy_test_util_common.cc b/net/spdy/spdy_test_util_common.cc
index ee8ad284a15e9572c4b0e51df21a0fa2fa18e8f7..c6efdfe05935b3618a8f21ce58c721d0d7fb3da8 100644
--- a/net/spdy/spdy_test_util_common.cc
+++ b/net/spdy/spdy_test_util_common.cc
@@ -292,7 +292,8 @@ bool MockECSignatureCreator::Sign(const uint8_t* data,
                                   int data_len,
                                   std::vector<uint8_t>* signature) {
   std::vector<uint8_t> private_key_value;
-  key_->ExportValue(&private_key_value);
+  if (!key_->ExportValueForTesting(&private_key_value))
+    return false;
   std::string head = "fakesignature";
   std::string tail = "/fakesignature";