Allow fallback from https to http for component update checks.

components/update_client/request_sender.h

Index: components/update_client/request_sender.h
diff --git a/components/update_client/request_sender.h b/components/update_client/request_sender.h
index 71b41ee538dc56f4d92b74fff9e0a5dc620d1e05..fc511f2a2a378b63408498d0729bc6451d3630ff 100644
--- a/components/update_client/request_sender.h
+++ b/components/update_client/request_sender.h
@@ -5,6 +5,8 @@
 #ifndef COMPONENTS_UPDATE_CLIENT_REQUEST_SENDER_H_
 #define COMPONENTS_UPDATE_CLIENT_REQUEST_SENDER_H_
 
+#include <stdint.h>
+
 #include <string>
 #include <vector>
 
@@ -32,8 +34,12 @@ class Configurator;
 class RequestSender : public net::URLFetcherDelegate {
  public:
   // If |error| is 0, then the response is provided in the |response| parameter.
-  using RequestSenderCallback =
-      base::Callback<void(int error, const std::string& response)>;
+  // |retry_after_sec| contains the value of the X-Retry-After response header,
+  // when the response was received from a cryptografically secure URL. The
+  // range for this value is [0, 86400], where the upper bound represents one
+  // day, and 0 means that no retry policy should be in effect.
+  using RequestSenderCallback = base::Callback<
+      void(int error, const std::string& response, int retry_after_sec)>;
 
   static int kErrorResponseNotTrusted;
 
@@ -54,9 +60,15 @@ class RequestSender : public net::URLFetcherDelegate {
   // Decodes and returns the public key used by CUP.
   static std::string GetKey(const char* key_bytes_base64);
 
-  // Returns the Etag of the server response or an empty string if the
-  // Etag is not available.
-  static std::string GetServerETag(const net::URLFetcher* source);
+  // Returns the string value of a header of the server response or an empty
+  // string if the header is not available.
+  static std::string GetStringHeaderValue(const net::URLFetcher* source,
+                                          const char* header_name);
+
+  // Returns the integral value of a header of the server response or -1 if
+  // if the header is not available or a conversion error has occured.
+  static int64_t GetInt64HeaderValue(const net::URLFetcher* source,
+                                     const char* header_name);
 
   // Overrides for URLFetcherDelegate.
   void OnURLFetchComplete(const net::URLFetcher* source) override;
@@ -68,10 +80,11 @@ class RequestSender : public net::URLFetcherDelegate {
   // contain the body and the etag associated with the HTTP response.
   void SendInternalComplete(int error,
                             const std::string& response_body,
-                            const std::string& response_etag);
+                            const std::string& response_etag,
+                            int retry_after_sec);
 
   // Helper function to handle a non-continuable error in Send.
-  void HandleSendError(int error);
+  void HandleSendError(int error, int retry_after_sec);
 
   base::ThreadChecker thread_checker_;