refactor: get default printer async

shell/browser/api/atom_api_web_contents.cc

@@ -113,11 +113,6 @@
 #include "ui/gfx/font_render_params.h"
 #endif
 
-#if BUILDFLAG(ENABLE_PRINTING)
-#include "chrome/browser/printing/print_view_manager_basic.h"
-#include "components/printing/common/print_messages.h"
-#endif
-
 #if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
 #include "shell/browser/extensions/atom_extension_web_contents_observer.h"
 #endif
@@ -346,6 +341,19 @@ base::Optional<base::TimeDelta> GetCursorBlinkInterval() {
   return base::nullopt;
 }
 
+#if BUILDFLAG(ENABLE_PRINTING)
+base::string16 GetDefaultPrinterAsync() {
+  base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
+                                                base::BlockingType::MAY_BLOCK);
+
+  scoped_refptr<printing::PrintBackend> backend =
+      printing::PrintBackend::CreateInstance(
+          nullptr, g_browser_process->GetApplicationLocale());
+  std::string printer_name = backend->GetDefaultPrinterName();
+  return base::UTF8ToUTF16(printer_name);
+}
+#endif
+
 }  // namespace
 
 WebContents::WebContents(v8::Isolate* isolate,
@@ -1713,6 +1721,25 @@ bool WebContents::IsCurrentlyAudible() {
 }
 
 #if BUILDFLAG(ENABLE_PRINTING)
+void WebContents::OnGetDefaultPrinter(
+    base::Value print_settings,
+    printing::CompletionCallback print_callback,
+    base::string16 device_name,
+    bool silent,
+    base::string16 default_printer) {
+  base::string16 printer_name =
+      device_name.empty() ? default_printer : device_name;
+  print_settings.SetStringKey(printing::kSettingDeviceName, printer_name);
+  auto* print_view_manager =
+      printing::PrintViewManagerBasic::FromWebContents(web_contents());
+  auto* focused_frame = web_contents()->GetFocusedFrame();
+  auto* rfh = focused_frame && focused_frame->HasSelection()
+                  ? focused_frame
+                  : web_contents()->GetMainFrame();
+  print_view_manager->PrintNow(rfh, silent, std::move(print_settings),
+                               std::move(print_callback));
+}
+
 void WebContents::Print(gin_helper::Arguments* args) {
   gin_helper::Dictionary options =
       gin::Dictionary::CreateEmpty(args->isolate());
@@ -1779,14 +1806,9 @@ void WebContents::Print(gin_helper::Arguments* args) {
 
   // We set the default to the system's default printer and only update
   // if at the Chromium level if the user overrides.
-  auto print_backend = printing::PrintBackend::CreateInstance(
-      nullptr, g_browser_process->GetApplicationLocale());
-  std::string default_printer = print_backend->GetDefaultPrinterName();
-  base::string16 device_name = base::UTF8ToUTF16(default_printer);
-
   // Printer device name as opened by the OS.
+  base::string16 device_name;
   options.Get("deviceName", &device_name);
-  settings.SetStringKey(printing::kSettingDeviceName, device_name);
 
   int scale_factor = 100;
   options.Get("scaleFactor", &scale_factor);
@@ -1866,14 +1888,13 @@ void WebContents::Print(gin_helper::Arguments* args) {
     settings.SetIntKey(printing::kSettingDpiVertical, dpi);
   }
 
-  auto* print_view_manager =
-      printing::PrintViewManagerBasic::FromWebContents(web_contents());
-  auto* focused_frame = web_contents()->GetFocusedFrame();
-  auto* rfh = focused_frame && focused_frame->HasSelection()
-                  ? focused_frame
-                  : web_contents()->GetMainFrame();
-  print_view_manager->PrintNow(rfh, silent, std::move(settings),
-                               std::move(callback));
+  base::PostTaskAndReplyWithResult(
+      FROM_HERE,
+      {base::ThreadPool(), base::MayBlock(), base::TaskPriority::USER_BLOCKING},
+      base::BindOnce(&GetDefaultPrinterAsync),
+      base::BindOnce(&WebContents::OnGetDefaultPrinter,
+                     weak_factory_.GetWeakPtr(), std::move(settings),
+                     std::move(callback), device_name, silent));
 }
 
 std::vector<printing::PrinterBasicInfo> WebContents::GetPrinterList() {

shell/browser/api/atom_api_web_contents.h

@@ -32,6 +32,8 @@
 #include "ui/gfx/image/image.h"
 
 #if BUILDFLAG(ENABLE_PRINTING)
+#include "chrome/browser/printing/print_view_manager_basic.h"
+#include "components/printing/common/print_messages.h"
 #include "printing/backend/print_backend.h"
 #include "shell/browser/printing/print_preview_message_handler.h"
 #endif
@@ -190,6 +192,11 @@ class WebContents : public gin_helper::TrackableObject<WebContents>,
   bool IsBeingCaptured();
 
 #if BUILDFLAG(ENABLE_PRINTING)
+  void OnGetDefaultPrinter(base::Value print_settings,
+                           printing::CompletionCallback print_callback,
+                           base::string16 device_name,
+                           bool silent,
+                           base::string16 default_printer);
   void Print(gin_helper::Arguments* args);
   std::vector<printing::PrinterBasicInfo> GetPrinterList();
   // Print current page as PDF.