QUIC - Initialize SourceAddressToken's timestamp_ in the constructor.

R=rch@chromium.org

Review URL: https://codereview.chromium.org/985383003

Cr-Commit-Position: refs/heads/master@{#319708}

net/quic/crypto/source_address_token.cc

@@ -12,7 +12,7 @@ using std::string;
 namespace net {
 
 SourceAddressToken::SourceAddressToken()
-    : has_cached_network_parameters_(false) {
+    : timestamp_(0), has_cached_network_parameters_(false) {
 }
 
 SourceAddressToken::~SourceAddressToken() {