Fix problem where images loaded using the background-image CSS attribute sometimes do not display on Mac after browsing back to the page (issue #447).

git-svn-id: https://chromiumembedded.googlecode.com/svn/trunk@403 5089003a-bbd8-11dd-ad1f-f1f9622dbc98

patch/patches/webcore_cachedresource.patch

@@ -0,0 +1,14 @@
+Index: CachedResource.cpp
+===================================================================
+--- CachedResource.cpp	(revision 100508)
++++ CachedResource.cpp	(working copy)
+@@ -365,6 +365,9 @@
+ 
+ void CachedResource::addClient(CachedResourceClient* client)
+ {
++    if (isPurgeable())
++        makePurgeable(false);
++  
+     addClientToSet(client);
+     didAddClient(client);
+ }