Add PrintPreviewStickySettings::GetRecentlyUsedPrinters()

Add method GetRecentlyUsedPrinters() for use with the CUPS proxy.

Bug: 1015662
Test: xvfb-run ./unit_tests --gtest_filter=PrintPreviewStickySettingsUnittest.*

Change-Id: I908f47d45259ab8dd941d320dad66275b95e00b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359729
Commit-Queue: Pranav Batra <batrapranav@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807228}

chrome/browser/printing/print_preview_sticky_settings.cc

@@ -57,6 +57,14 @@ void PrintPreviewStickySettings::RestoreFromPrefs(PrefService* prefs) {
 
 base::flat_map<std::string, int>
 PrintPreviewStickySettings::GetPrinterRecentlyUsedRanks() {
+  int current_rank = 0;
+  base::flat_map<std::string, int> recently_used_ranks;
+  for (const std::string& printer_id : GetRecentlyUsedPrinters())
+    recently_used_ranks[printer_id] = current_rank++;
+  return recently_used_ranks;
+}
+
+std::vector<std::string> PrintPreviewStickySettings::GetRecentlyUsedPrinters() {
   const std::string* sticky_settings_state = printer_app_state();
   if (!sticky_settings_state)
     return {};
@@ -71,15 +79,15 @@ PrintPreviewStickySettings::GetPrinterRecentlyUsedRanks() {
   if (!recent_destinations)
     return {};
 
-  base::flat_map<std::string, int> recently_used_ranks;
-  int current_rank = 0;
+  std::vector<std::string> printers;
+  printers.reserve(recent_destinations->GetList().size());
   for (const auto& recent_destination : recent_destinations->GetList()) {
     const std::string* printer_id = recent_destination.FindStringKey(kId);
     if (!printer_id)
       continue;
-    recently_used_ranks[*printer_id] = current_rank++;
+    printers.push_back(*printer_id);
   }
-  return recently_used_ranks;
+  return printers;
 }
 
 // static

chrome/browser/printing/print_preview_sticky_settings.h

@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_PRINTING_PRINT_PREVIEW_STICKY_SETTINGS_H_
 
 #include <string>
+#include <vector>
 
 #include "base/containers/flat_map.h"
 #include "base/optional.h"
@@ -43,6 +44,11 @@ class PrintPreviewStickySettings {
   // the rank the more recent the printer was used.
   base::flat_map<std::string, int> GetPrinterRecentlyUsedRanks();
 
+  // Parses serialized printing sticky settings state and extracts the list of
+  // recently used printers. The list is ordered from most recently used to
+  // least recently used.
+  std::vector<std::string> GetRecentlyUsedPrinters();
+
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
  private: