Simple fallback implementation.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 813f5c87ee873b58463dba7f81e32d0c2e7185b2..244b7250420f8b4ccaec75551eac575920cbec43 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1346,6 +1346,9 @@ const char kSimulateOutdated[]               = "simulate-outdated";
 // Replaces the buffered data source for <audio> and <video> with a simplified
 // resource loader that downloads the entire resource into memory.
 
+// Second origin that can be used for the spdy proxy.
+const char kSpdyProxyAuthFallback[]         = "spdy-proxy-auth-fallback";
+
 // Origin for which SpdyProxy authentication is supported.
 const char kSpdyProxyAuthOrigin[]           = "spdy-proxy-auth-origin";