Bug 1057688 - Skip doing a DNSPrefetch when LOAD_NO_NETWORK_IO or ONLY_FROM_CACHE flags are present r=mcmanus

netwerk/protocol/http/nsHttpChannel.cpp

@@ -4857,10 +4857,13 @@ nsHttpChannel::BeginConnect()
     if (mLoadFlags & VALIDATE_ALWAYS || BYPASS_LOCAL_CACHE(mLoadFlags))
         mCaps |= NS_HTTP_REFRESH_DNS;
 
-    if (!mConnectionInfo->UsingHttpProxy()) {
+    if (!mConnectionInfo->UsingHttpProxy() &&
+        !(mLoadFlags & (LOAD_NO_NETWORK_IO | LOAD_ONLY_FROM_CACHE))) {
         // Start a DNS lookup very early in case the real open is queued the DNS can
         // happen in parallel. Do not do so in the presence of an HTTP proxy as
         // all lookups other than for the proxy itself are done by the proxy.
+        // Also we don't do a lookup if the LOAD_NO_NETWORK_IO or
+        // LOAD_ONLY_FROM_CACHE flags are set.
         //
         // We keep the DNS prefetch object around so that we can retrieve
         // timing information from it. There is no guarantee that we actually