Bug 616414: Notify content processes when a pref has been cleared. r=dwitte

dom/ipc/ContentChild.cpp

@@ -492,6 +492,18 @@ ContentChild::RecvPreferenceUpdate(const PrefTuple& aPref)
     return true;
 }
 
+bool
+ContentChild::RecvClearUserPreference(const nsCString& aPrefName)
+{
+    nsCOMPtr<nsIPrefServiceInternal> prefs = do_GetService("@mozilla.org/preferences-service;1");
+    if (!prefs)
+        return false;
+
+    prefs->ClearContentPref(aPrefName);
+
+    return true;
+}
+
 bool
 ContentChild::RecvNotifyAlertsObserver(const nsCString& aType, const nsString& aData)
 {

dom/ipc/ContentChild.h

@@ -118,6 +118,7 @@ public:
     nsresult AddRemoteAlertObserver(const nsString& aData, nsIObserver* aObserver);
 
     virtual bool RecvPreferenceUpdate(const PrefTuple& aPref);
+    virtual bool RecvClearUserPreference(const nsCString& aPrefName);
 
     virtual bool RecvNotifyAlertsObserver(const nsCString& aType, const nsString& aData);
 

dom/ipc/ContentParent.cpp

@@ -372,14 +372,26 @@ ContentParent::Observe(nsISupports* aSubject,
         // We know prefs are ASCII here.
         NS_LossyConvertUTF16toASCII strData(aData);
 
-        PrefTuple pref;
         nsCOMPtr<nsIPrefServiceInternal> prefService =
           do_GetService("@mozilla.org/preferences-service;1");
 
-        prefService->MirrorPreference(strData, &pref);
-
-        if (!SendPreferenceUpdate(pref))
-            return NS_ERROR_NOT_AVAILABLE;
+        PRBool prefHasValue;
+        prefService->PrefHasUserValue(strData, &prefHasValue);
+        if (prefHasValue) {
+            // Pref was created, or previously existed and its value
+            // changed.
+            PrefTuple pref;
+            nsresult rv = prefService->MirrorPreference(strData, &pref);
+            NS_ASSERTION(NS_SUCCEEDED(rv), "Pref has value but can't mirror?");
+            if (!SendPreferenceUpdate(pref)) {
+                return NS_ERROR_NOT_AVAILABLE;
+            }
+        } else {
+            // Pref wasn't found.  It was probably removed.
+            if (!SendClearUserPreference(strData)) {
+                return NS_ERROR_NOT_AVAILABLE;
+            }
+        }
     }
     else if (!strcmp(aTopic, NS_IPC_IOSERVICE_SET_OFFLINE_TOPIC)) {
       NS_ConvertUTF16toUTF8 dataStr(aData);

dom/ipc/PContent.ipdl

@@ -104,6 +104,7 @@ child:
     async NotifyVisited(URI uri);
 
     PreferenceUpdate(PrefTuple pref);
+    ClearUserPreference(nsCString prefName);
 
     NotifyAlertsObserver(nsCString topic, nsString data);
 

modules/libpref/public/nsIPrefService.idl

@@ -163,7 +163,7 @@ interface nsIPrefService : nsISupports
 
 };
 
-[scriptable, uuid(37577836-e3fc-4a5e-b5d1-92a17fe0e7f7)]
+[scriptable, uuid(08c8cd2f-8345-45ee-938d-37ee6d3661b2)]
 interface nsIPrefServiceInternal : nsISupports
 {
   /**
@@ -181,7 +181,9 @@ interface nsIPrefServiceInternal : nsISupports
 
   [noscript] void mirrorPreferences(in nsPreferencesArrayPtr aArray);
   [noscript] void mirrorPreference(in ACString aPrefName, in nsPreferencePtr aPref);
+  [noscript] boolean prefHasUserValue(in ACString aPrefName);
   [noscript] void setPreference(in nsPreferencePtrConst aPref);
+  [noscript] void clearContentPref(in ACString aPrefName);
 };
 
 %{C++

modules/libpref/src/nsPrefService.cpp

@@ -350,11 +350,23 @@ NS_IMETHODIMP nsPrefService::ReadExtensionPrefs(nsILocalFile *aFile)
   return rv;
 }
 
+NS_IMETHODIMP nsPrefService::PrefHasUserValue(const nsACString& aPrefName,
+                                              PRBool* aHasValue)
+{
+  *aHasValue = PREF_HasUserPref(aPrefName.BeginReading());
+  return NS_OK;
+}
+
 NS_IMETHODIMP nsPrefService::SetPreference(const PrefTuple *aPref)
 {
   return pref_SetPrefTuple(*aPref, PR_TRUE);
 }
 
+NS_IMETHODIMP nsPrefService::ClearContentPref(const nsACString& aPrefName)
+{
+  return PREF_ClearUserPref(aPrefName.BeginReading());
+}
+
 NS_IMETHODIMP nsPrefService::MirrorPreference(const nsACString& aPrefName,
                                               PrefTuple *aPref)
 {