AU: Try delta updates first, then full updates

src/platform/update_engine/omaha_response_handler_action.h

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_OMAHA_RESPONSE_HANDLER_ACTION_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_OMAHA_RESPONSE_HANDLER_ACTION_H__
 
 #include <string>
 #include "update_engine/action.h"
 #include "update_engine/install_plan.h"
 #include "update_engine/update_check_action.h"
 
 // This class reads in an Omaha response and converts what it sees into
 // an install plan which is passed out.
 
 namespace chromeos_update_engine {
 
 class OmahaResponseHandlerAction;
 
 template<>
 class ActionTraits<OmahaResponseHandlerAction> {
  public:
   typedef UpdateCheckResponse InputObjectType;
   typedef InstallPlan OutputObjectType;
 };
 
 class OmahaResponseHandlerAction : public Action<OmahaResponseHandlerAction> {
  public:
-  OmahaResponseHandlerAction() {}
+  OmahaResponseHandlerAction() : got_no_update_response_(false) {}
   typedef ActionTraits<OmahaResponseHandlerAction>::InputObjectType
       InputObjectType;
   typedef ActionTraits<OmahaResponseHandlerAction>::OutputObjectType
       OutputObjectType;
   void PerformAction();
 
   // This is a synchronous action, and thus TerminateProcessing() should
   // never be called
   void TerminateProcessing() { CHECK(false); }
 
   // For unit-testing
   void set_boot_device(const std::string& boot_device) {
     boot_device_ = boot_device;
   }
+  
+  bool GotNoUpdateResponse() const { return got_no_update_response_; }
 
   // Debugging/logging
   static std::string StaticType() { return "OmahaResponseHandlerAction"; }
   std::string Type() const { return StaticType(); }
 
  private:
   // Assumes you want to install on the "other" device, where the other
   // device is what you get if you swap 1 for 2 or 3 for 4 or vice versa
   // for the number at the end of the boot device. E.g., /dev/sda1 -> /dev/sda2
   // or /dev/sda4 -> /dev/sda3
   static bool GetInstallDev(const std::string& boot_dev,
                             std::string* install_dev);
 
   // set to non-empty in unit tests
   std::string boot_device_;
+  
+  // True only if we got a response and the response said no updates
+  bool got_no_update_response_;
 
   DISALLOW_COPY_AND_ASSIGN(OmahaResponseHandlerAction);
 };
 
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_OMAHA_RESPONSE_HANDLER_ACTION_H__