Bug 725210 - Add observer notification for last PB docshell going away. r=bz

docshell/base/nsDocShell.cpp

@@ -242,6 +242,9 @@ static PRInt32 gNumberOfDocumentsLoading = 0;
 // Global count of existing docshells.
 static PRInt32 gDocShellCount = 0;
 
+// Global count of docshells with the private attribute set
+static PRUint32 gNumberOfPrivateDocShells = 0;
+
 // Global reference to the URI fixup service.
 nsIURIFixup *nsDocShell::sURIFixup = 0;
 
@@ -710,6 +713,19 @@ ConvertLoadTypeToNavigationType(PRUint32 aLoadType)
 
 static nsISHEntry* GetRootSHEntry(nsISHEntry *entry);
 
+static void
+DecreasePrivateDocShellCount()
+{
+    MOZ_ASSERT(gNumberOfPrivateDocShells > 0);
+    gNumberOfPrivateDocShells--;
+    if (!gNumberOfPrivateDocShells)
+    {
+        nsCOMPtr<nsIObserverService> obsvc = mozilla::services::GetObserverService();
+        if (obsvc)
+            obsvc->NotifyObservers(nsnull, "last-pb-context-exited", nsnull);
+    }
+}
+
 //*****************************************************************************
 //***    nsDocShell: Object Management
 //*****************************************************************************
@@ -818,6 +834,10 @@ nsDocShell::~nsDocShell()
                gNumberOfDocShells, mHistoryID);
     }
 #endif
+
+    if (mInPrivateBrowsing) {
+        DecreasePrivateDocShellCount();
+    }
 }
 
 nsresult
@@ -1999,8 +2019,15 @@ nsDocShell::GetUsePrivateBrowsing(bool* aUsePrivateBrowsing)
 NS_IMETHODIMP
 nsDocShell::SetUsePrivateBrowsing(bool aUsePrivateBrowsing)
 {
-    mInPrivateBrowsing = aUsePrivateBrowsing;
-
+    if (aUsePrivateBrowsing != mInPrivateBrowsing) {
+        mInPrivateBrowsing = aUsePrivateBrowsing;
+        if (aUsePrivateBrowsing) {
+            gNumberOfPrivateDocShells++;
+        } else {
+            DecreasePrivateDocShellCount();
+        }
+    }
+    
     PRInt32 count = mChildList.Count();
     for (PRInt32 i = 0; i < count; ++i) {
         nsCOMPtr<nsILoadContext> shell = do_QueryInterface(ChildAt(i));