Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/browser_process_impl.cc

Index: chrome/browser/browser_process_impl.cc
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index 01da7710d98d727e344531c916c8fab85118004e..c9874b3a8bce603965921723bec7cf951fb672b9 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -617,20 +617,14 @@ bool BrowserProcessImpl::plugin_finder_disabled() const {
     return false;
 }
 
-void BrowserProcessImpl::Observe(int type,
-                                 const content::NotificationSource& source,
-                                 const content::NotificationDetails& details) {
-  if (type == chrome::NOTIFICATION_PREF_CHANGED) {
-    std::string* pref = content::Details<std::string>(details).ptr();
-    if (*pref == prefs::kDefaultBrowserSettingEnabled) {
-      ApplyDefaultBrowserPolicy();
-    } else if (*pref == prefs::kDisabledSchemes) {
-      ApplyDisabledSchemesPolicy();
-    } else if (*pref == prefs::kAllowCrossOriginAuthPrompt) {
-      ApplyAllowCrossOriginAuthPromptPolicy();
-    }
-  } else {
-    NOTREACHED();
+void BrowserProcessImpl::OnPreferenceChanged(PrefServiceBase* service,
+                                             const std::string& pref) {
+  if (pref == prefs::kDefaultBrowserSettingEnabled) {
+    ApplyDefaultBrowserPolicy();
+  } else if (pref == prefs::kDisabledSchemes) {
+    ApplyDisabledSchemesPolicy();
+  } else if (pref == prefs::kAllowCrossOriginAuthPrompt) {
+    ApplyAllowCrossOriginAuthPromptPolicy();
   }
 }