Include USB printers in printer list as "provisional" devices.

chrome/browser/ui/webui/print_preview/print_preview_handler.cc

Index: chrome/browser/ui/webui/print_preview/print_preview_handler.cc
diff --git a/chrome/browser/ui/webui/print_preview/print_preview_handler.cc b/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
index 0567ac7303ada8a505bd78d3f192289d89cabfbf..3be7765d2e09a66fba97a310db91432bb86b81ed 100644
--- a/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
+++ b/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
@@ -27,6 +27,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
+#include "base/threading/worker_pool.h"
 #include "base/values.h"
 #include "chrome/browser/app_mode/app_mode_utils.h"
 #include "chrome/browser/browser_process.h"
@@ -45,6 +46,7 @@
 #include "chrome/browser/ui/browser_tabstrip.h"
 #include "chrome/browser/ui/chrome_select_file_policy.h"
 #include "chrome/browser/ui/scoped_tabbed_browser_displayer.h"
+#include "chrome/browser/ui/webui/print_preview/extension_printer_handler.h"
 #include "chrome/browser/ui/webui/print_preview/print_preview_ui.h"
 #include "chrome/browser/ui/webui/print_preview/printer_handler.h"
 #include "chrome/browser/ui/webui/print_preview/sticky_settings.h"
@@ -667,6 +669,10 @@ void PrintPreviewHandler::RegisterMessages() {
       base::Bind(&PrintPreviewHandler::HandleGetExtensionPrinters,
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback(
+      "getExtensionUsbPrinters",
+      base::Bind(&PrintPreviewHandler::HandleGetExtensionUsbPrinters,
+                 base::Unretained(this)));
+  web_ui()->RegisterMessageCallback(
       "getExtensionPrinterCapabilities",
       base::Bind(&PrintPreviewHandler::HandleGetExtensionPrinterCapabilities,
                  base::Unretained(this)));
@@ -744,6 +750,12 @@ void PrintPreviewHandler::HandleGetExtensionPrinters(
       &PrintPreviewHandler::OnGotPrintersForExtension, base::Unretained(this)));
 }
 
+void PrintPreviewHandler::HandleGetExtensionUsbPrinters(
+    const base::ListValue* args) {
+  extension_printer_handler_->StartGetUsbPrinters(base::Bind(

[Vitaly Buka (NO REVIEWS), 2015/05/27 16:58:40]

Can you avoid adding this function and remove as mach as possible 
USB related logic from PrintPreview.
I guess you can return combined list from
extension_printer_handler_->StartGetPrinters

[Vitaly Buka (NO REVIEWS), 2015/05/27 17:14:16]

I am asking because every new type of printers cause a lot of small changes in
different places of the preview JS.
I guess the only USB specific thing you need is a message for printers what
where never selected for users.

Also call you call that message some how generic? Something like "Printer
selection confirmation"
So if message is present, preview will ask user for any type of printers.

If HandleGetExtensionPrinterCapabilities is called after that,
extension_printer_handler_ will knows that user allowed access.

[Reilly Grant (use Gerrit), 2015/05/28 21:45:00]

Done.

+      &PrintPreviewHandler::OnGotExtensionUsbPrinters, base::Unretained(this)));
+}
+
 void PrintPreviewHandler::HandleGetExtensionPrinterCapabilities(
     const base::ListValue* args) {
   std::string printer_id;
@@ -1683,11 +1695,10 @@ void PrintPreviewHandler::FillPrinterDescription(
 #endif  // defined(ENABLE_SERVICE_DISCOVERY)
 
 void PrintPreviewHandler::EnsureExtensionPrinterHandlerSet() {
-  if (extension_printer_handler_.get())
-    return;
-
-  extension_printer_handler_ =
-      PrinterHandler::CreateForExtensionPrinters(Profile::FromWebUI(web_ui()));
+  if (!extension_printer_handler_.get()) {

[Vitaly Buka (NO REVIEWS), 2015/05/27 16:58:40]

if (extension_printer_handler_)

[Reilly Grant (use Gerrit), 2015/05/28 21:45:00]

Done.

+    extension_printer_handler_.reset(new ExtensionPrinterHandler(
+        Profile::FromWebUI(web_ui()), base::WorkerPool::GetTaskRunner(true)));
+  }
 }
 
 void PrintPreviewHandler::OnGotPrintersForExtension(
@@ -1697,6 +1708,11 @@ void PrintPreviewHandler::OnGotPrintersForExtension(
                                    base::FundamentalValue(done));
 }
 
+void PrintPreviewHandler::OnGotExtensionUsbPrinters(
+    const base::ListValue& printers) {
+  web_ui()->CallJavascriptFunction("onExtensionUsbPrintersAdded", printers);
+}
+
 void PrintPreviewHandler::OnGotExtensionPrinterCapabilities(
     const std::string& printer_id,
     const base::DictionaryValue& capabilities) {