Simple fallback implementation.

chrome/browser/net/spdyproxy/data_reduction_proxy_settings.cc

Index: chrome/browser/net/spdyproxy/data_reduction_proxy_settings.cc
diff --git a/chrome/browser/net/spdyproxy/data_reduction_proxy_settings.cc b/chrome/browser/net/spdyproxy/data_reduction_proxy_settings.cc
index 4318d770545b5b7eb7818aaf49d33ad3db4b43d6..c22869784fe5c96799959629e5d882489073424b 100644
--- a/chrome/browser/net/spdyproxy/data_reduction_proxy_settings.cc
+++ b/chrome/browser/net/spdyproxy/data_reduction_proxy_settings.cc
@@ -150,6 +150,21 @@ std::string DataReductionProxySettings::GetDataReductionProxyOrigin() {
 #endif
 }
 
+std::string DataReductionProxySettings::GetDataReductionProxyFallback() {
+  // Regardless of what else is defined, only return a value if the main proxy
+  // origin is defined.
+  if (GetDataReductionProxyOrigin().empty())
+    return std::string();
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  if (command_line.HasSwitch(switches::kSpdyProxyAuthFallback))
+    return command_line.GetSwitchValueASCII(switches::kSpdyProxyAuthFallback);
+#if defined(DATA_REDUCTION_FALLBACK_HOST)
+  return DATA_REDUCTION_FALLBACK_HOST;
+#else
+  return std::string();
+#endif
+}
+
 std::string DataReductionProxySettings::GetDataReductionProxyAuth() {
   if (!IsDataReductionProxyAllowed())
     return std::string();
@@ -237,17 +252,6 @@ void DataReductionProxySettings::OnURLFetchComplete(
   disabled_by_carrier_ = true;
 }
 
-std::string DataReductionProxySettings::GetDataReductionProxyOriginHostPort() {
-  std::string spdy_proxy = GetDataReductionProxyOrigin();
-  if (spdy_proxy.empty()) {
-    DLOG(ERROR) << "A SPDY proxy has not been set.";
-    return spdy_proxy;
-  }
-  // Remove a trailing slash from the proxy string if one exists as well as
-  // leading HTTPS scheme.
-  return net::HostPortPair::FromURL(GURL(spdy_proxy)).ToString();
-}
-
 void DataReductionProxySettings::OnIPAddressChanged() {
   if (enabled_by_user_) {
     DCHECK(IsDataReductionProxyAllowed());
@@ -324,12 +328,10 @@ void DataReductionProxySettings::MaybeActivateDataReductionProxy(
     ResetDataReductionStatistics();
   }
 
-  std::string spdy_proxy_origin = GetDataReductionProxyOriginHostPort();
-
+  std::string proxy = GetDataReductionProxyOrigin();
   // Configure use of the data reduction proxy if it is enabled and the proxy
   // origin is non-empty.
-  enabled_by_user_=
-      spdy_proxy_auth_enabled_.GetValue() && !spdy_proxy_origin.empty();
+  enabled_by_user_= spdy_proxy_auth_enabled_.GetValue() && !proxy.empty();
   SetProxyConfigs(enabled_by_user_ && !disabled_by_carrier_, at_startup);
 
   // Check if the proxy has been disabled explicitly by the carrier.
@@ -345,8 +347,11 @@ void DataReductionProxySettings::SetProxyConfigs(bool enabled,
   DictionaryPrefUpdate update(prefs, prefs::kProxy);
   base::DictionaryValue* dict = update.Get();
   if (enabled) {
+    std::string fallback = GetDataReductionProxyFallback();
     std::string proxy_server_config =
-        "http=" + GetDataReductionProxyOrigin() + ",direct://;";
+        "http=" + GetDataReductionProxyOrigin() +
+        (fallback.empty() ? "" : "," + fallback) +
+        ",direct://;";
     dict->SetString("server", proxy_server_config);
     dict->SetString("mode",
                     ProxyModeToString(ProxyPrefs::MODE_FIXED_SERVERS));