Register and select printer on click.

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

Index: chrome/browser/ui/webui/print_preview/printer_backend_proxy.cc
diff --git a/chrome/browser/ui/webui/print_preview/printer_backend_proxy.cc b/chrome/browser/ui/webui/print_preview/printer_backend_proxy.cc
index 9b316d5698c4ec05f98c5c4fbe30606e53698cc2..6e9d897c3e6f21e243deadf844e8471f216516d7 100644
--- a/chrome/browser/ui/webui/print_preview/printer_backend_proxy.cc
+++ b/chrome/browser/ui/webui/print_preview/printer_backend_proxy.cc
@@ -5,14 +5,28 @@
 #include "chrome/browser/ui/webui/print_preview/printer_backend_proxy.h"
 
 #include <string>
+#include <utility>
 
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
+#include "chrome/browser/ui/webui/print_preview/printer_capabilities.h"
 #include "content/public/browser/browser_thread.h"
 #include "printing/backend/print_backend.h"
 
 namespace printing {
 
+namespace {
+
+void PostCallbackOnUIThread(const PrinterSetupCallback& cb,
+                            std::unique_ptr<base::DictionaryValue> result) {
+  content::BrowserThread::PostTask(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(cb, base::Passed(std::move(result))));

[Lei Zhang, 2016/11/03 23:41:46]

Also less verbose if std::move(result) is removed in favor of &result.

[skau, 2016/11/04 19:28:59]

Switched to PostTaskAndReply.  Code has been removed.

+}
+
+}  // namespace
+
 std::string GetDefaultPrinterOnBlockingPoolThread() {
   DCHECK(content::BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
 
@@ -36,4 +50,30 @@ PrinterList EnumeratePrintersOnBlockingPoolThread(Profile* /* profile */) {
   return printer_list;
 }
 
+void ConfigurePrinterAndFetchCapabilities(Profile* /* profile */,
+                                          const std::string& device_name,
+                                          const PrinterSetupCallback& cb) {
+  DCHECK(content::BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
+
+  scoped_refptr<printing::PrintBackend> print_backend(
+      printing::PrintBackend::CreateInstance(nullptr));
+
+  VLOG(1) << "Get printer capabilities start for " << device_name;
+
+  std::unique_ptr<base::DictionaryValue> printer_info;
+  if (!print_backend->IsValidPrinter(device_name)) {
+    LOG(WARNING) << "Invalid printer " << device_name;
+    PostCallbackOnUIThread(cb, nullptr);

[Lei Zhang, 2016/11/03 23:41:46]

An alternative to having PostCallbackOnUIThread() is to have a helper function
that returns std::unique_ptr<base::DictionaryValue> do most of the work. Then
ConfigurePrinterAndFetchCapabilities() just has to call that, and take the
result and do a PostTask(). That way, will be less likely to forget to run the
callback.

[skau, 2016/11/04 19:28:59]

Thanks.  I've done that and it is simpler now.

+    return;
+  }
+
+  PrinterBasicInfo basic_info;
+  if (!print_backend->GetPrinterBasicInfo(device_name, &basic_info)) {
+    PostCallbackOnUIThread(cb, nullptr);
+    return;
+  }
+
+  PostCallbackOnUIThread(cb, GetSettingsDictionary(device_name, basic_info));
+}
+
 }  // namespace printing