Fix bug 399185 -- Make image request URIs immutable so that we don't have to

clone them later.  r=jst, sr=biesi, a=vlad

content/base/public/nsContentUtils.h

@@ -557,6 +557,8 @@ public:
                              PRInt16* aImageBlockingStatus = nsnull);
   /**
    * Method to start an image load.  This does not do any security checks.
+   * This method will attempt to make aURI immutable; a caller that wants to
+   * keep a mutable version around should pass in a clone.
    *
    * @param aURI uri of the image to be loaded
    * @param aLoadingDocument the document we belong to

content/base/src/nsContentUtils.cpp

@@ -2157,6 +2157,9 @@ nsContentUtils::LoadImage(nsIURI* aURI, nsIDocument* aLoadingDocument,
 
   nsIURI *documentURI = aLoadingDocument->GetDocumentURI();
 
+  // Make the URI immutable so people won't change it under us
+  NS_TryToSetImmutable(aURI);
+
   // We don't use aLoadingPrincipal for anything here yet... but we
   // will.  See bug 377092.