Correctly clear deprecated "proxy" pref set by data reduction proxy.

chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.cc

Index: chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.cc
diff --git a/chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.cc b/chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.cc
index ce1f7c96096ffd7cfbd2c5fd8857c227b0b4cf9e..1297c623d29fc3aee810d8cd2f9a392bf8b5c1a8 100644
--- a/chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.cc
+++ b/chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.cc
@@ -30,8 +30,17 @@ using data_reduction_proxy::DataReductionProxySettings;
 // hierarchy. This method removes the Data Reduction Proxy configuration from
 // prefs, if present. |proxy_pref_name| is the name of the proxy pref.
 void MigrateDataReductionProxyOffProxyPrefs(PrefService* prefs) {
-  DictionaryPrefUpdate update(prefs, prefs::kProxy);
-  base::DictionaryValue* dict = update.Get();
+  base::DictionaryValue* dict =
+      (base::DictionaryValue*) prefs->GetUserPrefValue(prefs::kProxy);
+  if (!dict)
+    return;
+
+  // Clear empty "proxy" dictionary created by a bug. See http://crbug/448172
+  if (dict->empty()) {
+    prefs->ClearPref(prefs::kProxy);
+    return;
+  }
+
   std::string mode;
   if (!dict->GetString("mode", &mode))
     return;
@@ -46,9 +55,7 @@ void MigrateDataReductionProxyOffProxyPrefs(PrefService* prefs) {
           ContainsDataReductionProxy(proxy_rules)) {
     return;
   }
-  dict->SetString("mode", ProxyModeToString(ProxyPrefs::MODE_SYSTEM));

[bengr, 2015/02/04 00:09:50]

Should we also clear the pref if we encounter this setting?

[Not at Google. Contact bengr, 2015/02/04 00:44:14]

Safer not to, especially if we are patching this to M41.

As the cl stands, it will remove all "proxy" entries set by data reduction
proxy. Not sure we gain anything by clearing settings set by other components.

Although I do agree that no one should have to set mode to "system" since it is
the default.

-  dict->SetString("server", "");
-  dict->SetString("bypass_list", "");
+  prefs->ClearPref(prefs::kProxy);
 }
 
 DataReductionProxyChromeSettings::DataReductionProxyChromeSettings(