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 7cb72c1ecb80a639cff7f9cabfd3723f9fb5f6a8..aacfea084f52763a872a6022f1ea9a1d59575ed5 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -610,20 +610,14 @@ safe_browsing::ClientSideDetectionService*
   return NULL;
 }
 
-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();
   }
 }