Have net-export's save dialog default to last used save directory

chrome/browser/ui/webui/net_export_ui.cc

 // Copyright (c) 2013 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/ui/webui/net_export_ui.h"
 
 #include <memory>
 #include <string>
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
+#include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/browser_process.h"
+#include "chrome/browser/download/download_prefs.h"
 #include "chrome/browser/platform_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/chrome_select_file_policy.h"
 #include "chrome/common/features.h"
 #include "chrome/common/url_constants.h"
 #include "components/grit/components_resources.h"
 #include "components/net_log/chrome_net_log.h"
 #include "components/net_log/net_export_ui_constants.h"
 #include "components/net_log/net_log_file_writer.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/url_data_source.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_ui.h"
 #include "content/public/browser/web_ui_data_source.h"
 #include "content/public/browser/web_ui_message_handler.h"
 #include "ui/shell_dialogs/select_file_dialog.h"
 
 #if BUILDFLAG(ANDROID_JAVA_UI)
 #include "chrome/browser/android/intent_helper.h"
 #endif
 
 using content::BrowserThread;
 using content::WebContents;
 using content::WebUIMessageHandler;
 
 namespace {
 
+base::LazyInstance<base::FilePath>::Leaky
+    last_save_dir = LAZY_INSTANCE_INITIALIZER;

[mmenke, 2016/11/17 18:50:50]

Comment that this may only be accessed on the UI thread?  And also add 
DCHECK_CURRENTLY_ON(content::BrowserThread::UI); at the start of both methods
that access it?

Unsafe to read/write to it on multiple threads.

[wangyix, 2016/11/17 19:46:15]

Done.

+
 content::WebUIDataSource* CreateNetExportHTMLSource() {
   content::WebUIDataSource* source =
       content::WebUIDataSource::Create(chrome::kChromeUINetExportHost);
 
   source->SetJsonPath("strings.js");
   source->AddResourcePath(net_log::kNetExportUIJS, IDR_NET_LOG_NET_EXPORT_JS);
   source->SetDefaultResource(IDR_NET_LOG_NET_EXPORT_HTML);
   return source;
 }
 
@@ skipping 133 matching lines @@
                  weak_ptr_factory_.GetWeakPtr(), net_log_file_writer_));
 }
 
 void NetExportMessageHandler::OnStartNetLog(const base::ListValue* list) {
   bool result = list->GetString(0, &log_mode_);
   DCHECK(result);
 
   if (UsingMobileUI()) {
     StartNetLog();
   } else {
-    base::FilePath home_dir = base::GetHomeDir();
-    base::FilePath default_path =
-        home_dir.Append(FILE_PATH_LITERAL("chrome-net-export-log.json"));
-    ShowSelectFileDialog(default_path);
+    base::FilePath initial_dir = last_save_dir.Pointer()->empty() ?
+        DownloadPrefs::FromBrowserContext(
+            web_ui()->GetWebContents()->GetBrowserContext())->DownloadPath() :
+        *last_save_dir.Pointer();
+    base::FilePath initial_path =
+        initial_dir.Append(FILE_PATH_LITERAL("chrome-net-export-log.json"));
+    ShowSelectFileDialog(initial_path);
   }
 }
 
 void NetExportMessageHandler::OnStopNetLog(const base::ListValue* list) {
   ProcessNetLogCommand(weak_ptr_factory_.GetWeakPtr(), net_log_file_writer_,
                        net_log::NetLogFileWriter::DO_STOP);
 }
 
 void NetExportMessageHandler::OnSendNetLog(const base::ListValue* list) {
   content::BrowserThread::PostTaskAndReplyWithResult(
@@ skipping 117 matching lines @@
       ui::SelectFileDialog::SELECT_SAVEAS_FILE, base::string16(), default_path,
       &file_type_info, 0, base::FilePath::StringType(), owning_window, nullptr);
 }
 
 void NetExportMessageHandler::FileSelected(const base::FilePath& path,
                                            int index,
                                            void* params) {
   DCHECK(select_file_dialog_);
   select_file_dialog_ = nullptr;
 
+  *last_save_dir.Pointer() = path.DirName();
   BrowserThread::PostTaskAndReply(
       BrowserThread::FILE_USER_BLOCKING, FROM_HERE,
       base::Bind(&net_log::NetLogFileWriter::SetUpNetExportLogPath,
                  base::Unretained(net_log_file_writer_), path),
       // NetExportMessageHandler is tied to the lifetime of the tab
       // so it cannot be assured that it will be valid when this
       // StartNetLog is called. Instead of using base::Unretained a
       // weak pointer is used to adjust for this.
       base::Bind(&NetExportMessageHandler::StartNetLog,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
 void NetExportMessageHandler::FileSelectionCanceled(void* params) {
   DCHECK(select_file_dialog_);
   select_file_dialog_ = nullptr;
 }
 
 }  // namespace
 
 NetExportUI::NetExportUI(content::WebUI* web_ui) : WebUIController(web_ui) {
   web_ui->AddMessageHandler(new NetExportMessageHandler());
 
   // Set up the chrome://net-export/ source.
   Profile* profile = Profile::FromWebUI(web_ui);
   content::WebUIDataSource::Add(profile, CreateNetExportHTMLSource());
 }