Introduce ERR_NETWORK_CHANGED and allow URLFetcher to automatically retry on that error.

net/base/mock_host_resolver.cc

Index: net/base/mock_host_resolver.cc
diff --git a/net/base/mock_host_resolver.cc b/net/base/mock_host_resolver.cc
index d86e20924c538c1bb1ce40c16840b07e9c4dcef4..17704aa059f7d90fb32262074eb2fa102ebc79a6 100644
--- a/net/base/mock_host_resolver.cc
+++ b/net/base/mock_host_resolver.cc
@@ -84,10 +84,13 @@ int MockHostResolverBase::Resolve(const RequestInfo& info,
   requests_[id] = req;
   if (handle)
     *handle = reinterpret_cast<RequestHandle>(id);
-  MessageLoop::current()->PostTask(FROM_HERE,
-                                   base::Bind(&MockHostResolverBase::ResolveNow,
-                                              AsWeakPtr(),
-                                              id));
+
+  if (resolve_automatically_) {
+    MessageLoop::current()->PostTask(
+        FROM_HERE,
+        base::Bind(&MockHostResolverBase::ResolveNow, AsWeakPtr(), id));
+  }
+
   return ERR_IO_PENDING;
 }
 
@@ -117,9 +120,21 @@ HostCache* MockHostResolverBase::GetHostCache() {
   return cache_.get();
 }
 
+void MockHostResolverBase::ResolveAllPending() {
+  DCHECK(CalledOnValidThread());
+  DCHECK(!resolve_automatically_);
+  for (RequestMap::iterator i = requests_.begin(); i != requests_.end(); ++i) {
+    MessageLoop::current()->PostTask(
+        FROM_HERE,
+        base::Bind(&MockHostResolverBase::ResolveNow, AsWeakPtr(), i->first));
+  }
+}
+
 // start id from 1 to distinguish from NULL RequestHandle
 MockHostResolverBase::MockHostResolverBase(bool use_caching)
-    : synchronous_mode_(false), next_request_id_(1) {
+    : synchronous_mode_(false),
+      resolve_automatically_(true),
+      next_request_id_(1) {
   rules_ = CreateCatchAllHostResolverProc();
 
   if (use_caching) {