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

net/base/mock_host_resolver.h

Index: net/base/mock_host_resolver.h
diff --git a/net/base/mock_host_resolver.h b/net/base/mock_host_resolver.h
index 033cf147527769bbd3a9cd7eae464a7a7b306037..a2c82c7bff0da8ca51eeacba3d7b9eb9d1d57936 100644
--- a/net/base/mock_host_resolver.h
+++ b/net/base/mock_host_resolver.h
@@ -65,6 +65,14 @@ class MockHostResolverBase : public HostResolver,
     synchronous_mode_ = is_synchronous;
   }
 
+  // Asynchronous requests are automatically resolved when this is set to true,
+  // which is the default. When set to false, Resolve() returns IO_PENDING and
+  // ResolveAllPending() must be explicitly invoked to resolve all requests that
+  // are pending.
+  void set_resolve_automatically(bool resolve_automatically) {
+    resolve_automatically_ = resolve_automatically;
+  }
+
   // HostResolver methods:
   virtual int Resolve(const RequestInfo& info,
                       AddressList* addresses,
@@ -77,6 +85,15 @@ class MockHostResolverBase : public HostResolver,
   virtual void CancelRequest(RequestHandle req) OVERRIDE;
   virtual HostCache* GetHostCache() OVERRIDE;
 
+  // Resolves all pending requests. It is only valid to invoked this if
+  // set_resolve_automatically(false) was set before. The requests are resolved
+  // asynchronously, after this call returns.
+  void ResolveAllPending();
+
+  // Returns true if there are pending requests that can be resolved by invoking
+  // ResolveAllPending().
+  bool has_pending_requests() const { return !requests_.empty(); }
+
  protected:
   explicit MockHostResolverBase(bool use_caching);
 
@@ -94,6 +111,7 @@ class MockHostResolverBase : public HostResolver,
   void ResolveNow(size_t id);
 
   bool synchronous_mode_;
+  bool resolve_automatically_;
   scoped_refptr<RuleBasedHostResolverProc> rules_;
   scoped_ptr<HostCache> cache_;
   RequestMap requests_;