[CUPS] Implement the Webui handler for the printers auto discovery.

chromeos/printing/fake_printer_discoverer.cc

 // Copyright 2016 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.
 
 #include "chromeos/printing/fake_printer_discoverer.h"
 
 #include <algorithm>
 #include <iterator>
 #include <memory>
 
@@ skipping 56 matching lines @@
     printers_[i].set_manufacturer("Chromium");
     printers_[i].set_model(i % 3 == 0 ? "Inkjet" : "Laser Maker");
     printers_[i].set_uri(
         base::StringPrintf("lpr://192.168.1.%d:9100/bldg/printer", i));
     printers_[i].set_uuid(
         base::StringPrintf("UUID-%4d-%4d-%4d-UUID", i * 3, i * 2, i));
   }
 }
 
 void FakePrinterDiscoverer::EmitPrinters(size_t start, size_t end) {
-  if (!discovery_running_ || start >= printers_.size() || end > start)
+  if (!discovery_running_ || start >= printers_.size() || end < start)
     return;
 
   size_t clipped_start = std::max(static_cast<size_t>(0), start);
   size_t clipped_end = std::min(printers_.size(), end);
   if (!observers_.empty()) {
     std::vector<Printer> subset(printers_.cbegin() + clipped_start,
                                 printers_.cbegin() + clipped_end);
 
     for (auto observer : observers_)
       observer->OnPrintersFound(subset);
   }
 
   // schedule another emit if elements remain.
   if (end < printers_.size()) {
     base::SequencedTaskRunnerHandle::Get()->PostNonNestableDelayedTask(
         FROM_HERE,
         base::Bind(&FakePrinterDiscoverer::EmitPrinters,
                    weak_ptr_factory_.GetWeakPtr(), clipped_end, end + end),
         base::TimeDelta::FromMilliseconds(2000));
   } else {
     // We're done.  Notify observers.
     discovery_running_ = false;
     for (auto observer : observers_)
       observer->OnDiscoveryDone();
   }
 }
 
 }  // namespace chromeos