Merge 105226 - Ensure we don't cancel revalidation of a CachedResource

Source/WebCore/loader/cache/CachedResource.cpp

Index: Source/WebCore/loader/cache/CachedResource.cpp
===================================================================
--- Source/WebCore/loader/cache/CachedResource.cpp	(revision 105796)
+++ Source/WebCore/loader/cache/CachedResource.cpp	(working copy)
@@ -139,6 +139,7 @@
     , m_requestedFromNetworkingLayer(false)
     , m_inCache(false)
     , m_loading(false)
+    , m_switchingClientsToRevalidatedResource(false)
     , m_type(type)
     , m_status(Pending)
 #ifndef NDEBUG
@@ -520,6 +521,9 @@
 void CachedResource::clearResourceToRevalidate() 
 { 
     ASSERT(m_resourceToRevalidate);
+    if (m_switchingClientsToRevalidatedResource)
+        return;
+
     // A resource may start revalidation before this method has been called, so check that this resource is still the proxy resource before clearing it out.
     if (m_resourceToRevalidate->m_proxyResource == this) {
         m_resourceToRevalidate->m_proxyResource = 0;
@@ -538,6 +542,7 @@
 
     LOG(ResourceLoading, "CachedResource %p switchClientsToRevalidatedResource %p", this, m_resourceToRevalidate);
 
+    m_switchingClientsToRevalidatedResource = true;
     HashSet<CachedResourceHandleBase*>::iterator end = m_handlesToRevalidate.end();
     for (HashSet<CachedResourceHandleBase*>::iterator it = m_handlesToRevalidate.begin(); it != end; ++it) {
         CachedResourceHandleBase* handle = *it;
@@ -565,10 +570,14 @@
     for (unsigned n = 0; n < moveCount; ++n)
         m_resourceToRevalidate->addClientToSet(clientsToMove[n]);
     for (unsigned n = 0; n < moveCount; ++n) {
+        // Calling didAddClient may do anything, including trying to cancel revalidation.
+        // Assert that it didn't succeed.
+        ASSERT(m_resourceToRevalidate);
         // Calling didAddClient for a client may end up removing another client. In that case it won't be in the set anymore.
         if (m_resourceToRevalidate->m_clients.contains(clientsToMove[n]))
             m_resourceToRevalidate->didAddClient(clientsToMove[n]);
     }
+    m_switchingClientsToRevalidatedResource = false;
 }
     
 void CachedResource::updateResponseAfterRevalidation(const ResourceResponse& validatingResponse)