Make URLDataSource::GetSource() const.

chrome/browser/ui/webui/chromeos/proxy_settings_ui.cc

Index: chrome/browser/ui/webui/chromeos/proxy_settings_ui.cc
diff --git a/chrome/browser/ui/webui/chromeos/proxy_settings_ui.cc b/chrome/browser/ui/webui/chromeos/proxy_settings_ui.cc
index e4b8e17b13fe8c7759443c437af19d8868ab9875..207c40c6e32be4c4fdca4310a4a1751c8b998cc8 100644
--- a/chrome/browser/ui/webui/chromeos/proxy_settings_ui.cc
+++ b/chrome/browser/ui/webui/chromeos/proxy_settings_ui.cc
@@ -33,7 +33,7 @@ class ProxySettingsHTMLSource : public content::URLDataSource {
   explicit ProxySettingsHTMLSource(DictionaryValue* localized_strings);
 
   // content::URLDataSource implementation.
-  virtual std::string GetSource() OVERRIDE;
+  virtual std::string GetSource() const OVERRIDE;
   virtual void StartDataRequest(
       const std::string& path,
       bool is_incognito,
@@ -59,7 +59,7 @@ ProxySettingsHTMLSource::ProxySettingsHTMLSource(
     : localized_strings_(localized_strings) {
 }
 
-std::string ProxySettingsHTMLSource::GetSource() {
+std::string ProxySettingsHTMLSource::GetSource() const {
   return chrome::kChromeUIProxySettingsHost;
 }