Fix -Wreorder compile error after https://codereview.webrtc.org/1189583002/

BUG=webrtc:4685, webrtc:4686
TBR=torbjorng@chromium.org,

Review URL: https://codereview.webrtc.org/1300683002 .

Cr-Commit-Position: refs/heads/master@{#9720}

webrtc/base/nssidentity.h

@@ -56,9 +56,9 @@ class NSSKeyPair {
   SSLKEAType ssl_kea_type() const { return ssl_kea_type_; }
 
  private:
-  SSLKEAType ssl_kea_type_;
   SECKEYPrivateKey* privkey_;
   SECKEYPublicKey* pubkey_;
+  SSLKEAType ssl_kea_type_;
 
   DISALLOW_COPY_AND_ASSIGN(NSSKeyPair);
 };