porting patch from imageblocker to contentblocker.

already had r=dwitte, sr=shaver. bug 256172

extensions/permissions/nsContentBlocker.cpp

@@ -259,6 +259,20 @@ nsContentBlocker::TestPermission(nsIURI *aCurrentURI,
   case BEHAVIOR_NOFOREIGN:
     // Third party checking
 
+    // Need a requesting uri for third party checks to work.
+    if (!aFirstURI)
+      return NS_OK;
+
+    PRBool trustedSource = PR_FALSE;
+    rv = aFirstURI->SchemeIs("chrome", &trustedSource);
+    NS_ENSURE_SUCCESS(rv,rv);
+    if (!trustedSource) {
+      rv = aFirstURI->SchemeIs("resource", &trustedSource);
+      NS_ENSURE_SUCCESS(rv,rv);
+    }
+    if (trustedSource)
+      return NS_OK;
+
     // compare tails of names checking to see if they have a common domain
     // we do this by comparing the tails of both names where each tail 
     // includes at least one dot