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

chrome/browser/ui/webui/net_export_ui.cc

Index: chrome/browser/ui/webui/net_export_ui.cc
diff --git a/chrome/browser/ui/webui/net_export_ui.cc b/chrome/browser/ui/webui/net_export_ui.cc
index 8ac8368d50813a077127c3847534ffaed689375e..8caf3f16282486f503db69c8b69a383e28e5c916 100644
--- a/chrome/browser/ui/webui/net_export_ui.cc
+++ b/chrome/browser/ui/webui/net_export_ui.cc
@@ -9,6 +9,7 @@
 
 #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"
@@ -41,6 +42,9 @@ using content::WebUIMessageHandler;
 
 namespace {
 
+base::LazyInstance<base::FilePath>::Leaky
+    last_save_dir = LAZY_INSTANCE_INITIALIZER;
+
 content::WebUIDataSource* CreateNetExportHTMLSource() {
   content::WebUIDataSource* source =
       content::WebUIDataSource::Create(chrome::kChromeUINetExportHost);
@@ -194,10 +198,12 @@ void NetExportMessageHandler::OnStartNetLog(const base::ListValue* list) {
   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() ? base::GetHomeDir()
+                                         : *last_save_dir.Pointer();
+    base::FilePath initial_path =
+        initial_dir.Append(FILE_PATH_LITERAL("chrome-net-export-log.json"));
+    ShowSelectFileDialog(initial_path);

[mmenke, 2016/10/24 17:04:55]

This will show the home directory every time Chrome is restarted.

What's the behavior if we just use an empty path?  On Windows, I suspect it will
show us the path wherever the last file dialog was open at, which is preserved
across browser restarts, which would probably be superior behavior.  Not sure
about other platforms, though.

[wangyix, 2016/10/24 23:35:15]

I'm working on Goobuntu, and the behavior is the following:
When the dialog is first opened after starting chrome, it defaults to listing
"recently used" folders. After the first save, it defaults to the last saved
location, as desired.  However, the last saved location is not preserved across
browser restarts.

   }
 }
 
@@ -327,6 +333,7 @@ void NetExportMessageHandler::ShowSelectFileDialog(
   gfx::NativeWindow owning_window =
       webcontents ? webcontents->GetTopLevelNativeWindow()
                   : nullptr;
+
   select_file_dialog_->SelectFile(
       ui::SelectFileDialog::SELECT_SAVEAS_FILE, base::string16(), default_path,
       &file_type_info, 0, base::FilePath::StringType(), owning_window, nullptr);
@@ -336,6 +343,8 @@ void NetExportMessageHandler::FileSelected(const base::FilePath& path,
                                            int index,
                                            void* params) {
   select_file_dialog_ = nullptr;
+  *last_save_dir.Pointer() = path.DirName();
+
   BrowserThread::PostTaskAndReply(
       BrowserThread::FILE_USER_BLOCKING, FROM_HERE,
       base::Bind(&net_log::NetLogFileWriter::SetUpNetExportLogPath,