Introduce a delegate to avoid hardcoding "chrome-extension" in net/.

net/base/network_delegate.h

Index: net/base/network_delegate.h
diff --git a/net/base/network_delegate.h b/net/base/network_delegate.h
index 2886d486d91ddf7797c914b0ea68fc1e7a27711d..4d56e3f6cfcd4750a8a703c2a655e2520b6d222c 100644
--- a/net/base/network_delegate.h
+++ b/net/base/network_delegate.h
@@ -85,6 +85,7 @@ class NetworkDelegate : public base::NonThreadSafe {
                     CookieOptions* options);
   bool CanAccessFile(const URLRequest& request,
                      const FilePath& path) const;
+  bool CanThrottleRequest(const URLRequest& request) const;
 
  private:
   // This is the interface for subclasses of NetworkDelegate to implement. These
@@ -202,6 +203,10 @@ class NetworkDelegate : public base::NonThreadSafe {
   virtual bool OnCanAccessFile(const URLRequest& request,
                                const FilePath& path) const = 0;
 
+  // Returns true if the given request may be rejected when the
+  // URLRequestThrottlerManager believes the server servicing the
+  // request is overloaded or down.
+  virtual bool OnCanThrottleRequest(const URLRequest& request) const = 0;
 };
 
 }  // namespace net