Make CUPS USB printing play better with the settings page. This change does several things:

chrome/browser/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 "chrome/browser/chromeos/printing/fake_printer_discoverer.h"
-
-#include <algorithm>
-#include <iterator>
-#include <memory>
-
-#include "base/bind.h"
-#include "base/memory/ptr_util.h"
-#include "base/strings/stringprintf.h"
-#include "base/threading/sequenced_task_runner_handle.h"
-#include "base/time/time.h"
-#include "chrome/browser/chromeos/printing/printer_discoverer.h"
-
-namespace chromeos {
-
-// static
-std::unique_ptr<PrinterDiscoverer> PrinterDiscoverer::Create() {
-  return base::MakeUnique<FakePrinterDiscoverer>();
-}
-
-FakePrinterDiscoverer::~FakePrinterDiscoverer() {}
-
-bool FakePrinterDiscoverer::StartDiscovery() {
-  discovery_running_ = true;
-
-  for (auto* observer : observers_)
-    observer->OnDiscoveryStarted();
-
-  base::SequencedTaskRunnerHandle::Get()->PostNonNestableDelayedTask(
-      FROM_HERE, base::Bind(&FakePrinterDiscoverer::EmitPrinters,
-                            weak_ptr_factory_.GetWeakPtr(), 0, 2),
-      base::TimeDelta::FromMilliseconds(2000));
-  return true;
-}
-
-bool FakePrinterDiscoverer::StopDiscovery() {
-  discovery_running_ = false;
-  for (auto* observer : observers_)
-    observer->OnDiscoveryStopping();
-
-  return true;
-}
-
-void FakePrinterDiscoverer::AddObserver(PrinterDiscoverer::Observer* observer) {
-  auto found = std::find(observers_.begin(), observers_.end(), observer);
-  if (found == observers_.end())
-    observers_.push_back(observer);
-}
-
-void FakePrinterDiscoverer::RemoveObserver(
-    PrinterDiscoverer::Observer* observer) {
-  auto found = std::find(observers_.begin(), observers_.end(), observer);
-  if (found != observers_.end())
-    observers_.erase(found);
-}
-
-FakePrinterDiscoverer::FakePrinterDiscoverer()
-    : discovery_running_(false), weak_ptr_factory_(this) {
-  for (int i = 0; i < 12; i++) {
-    // printer doesn't have a ppd
-    printers_.emplace_back(base::StringPrintf("GUID%2d", i));
-    printers_[i].set_display_name(base::StringPrintf("PrinterName%2d", i));
-    printers_[i].set_description(
-        base::StringPrintf("Printer%2dDescription", i));
-    printers_[i].set_manufacturer("Chromium");
-    printers_[i].set_model(i % 3 == 0 ? "Inkjet" : "Laser Maker");
-    printers_[i].set_uri(
-        base::StringPrintf("lpd://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)
-    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