Delay generation of User-Agent header to URLRequestHttpJob and accept custom User-Agent from XHR/Fe…

net/url_request/url_request.h

Index: net/url_request/url_request.h
diff --git a/net/url_request/url_request.h b/net/url_request/url_request.h
index 005ae29d2cbc2627e869c4f65e99ba52393d5941..96e392b03931b87e18b14d9fe1a8e1d6f558abe7 100644
--- a/net/url_request/url_request.h
+++ b/net/url_request/url_request.h
@@ -356,6 +356,10 @@ class NET_EXPORT URLRequest : NON_EXPORTED_BASE(public base::NonThreadSafe),
     return extra_request_headers_;
   }
 
+  void set_default_user_agent(const std::string& default_user_agent);
+  const std::string& default_user_agent() const { return default_user_agent_; }
+  bool has_default_user_agent() const;
+
   // Gets the full request headers sent to the server.
   //
   // Return true and overwrites headers if it can get the request headers;
@@ -763,6 +767,8 @@ class NET_EXPORT URLRequest : NON_EXPORTED_BASE(public base::NonThreadSafe),
   std::string token_binding_referrer_;
   FirstPartyURLPolicy first_party_url_policy_;
   HttpRequestHeaders extra_request_headers_;
+  bool has_default_user_agent_;

[horo, 2016/08/21 08:39:37]

You can use base::Optional<std::string>.

[mmenke, 2016/08/21 14:37:39]

Given that URLRequest uses empty strings to denote arguments it should ignore,
I'd say just stick with an empty string, for consistency.

+  std::string default_user_agent_;
   int load_flags_;  // Flags indicating the request type for the load;
                     // expected values are LOAD_* enums above.