Fix crash upon opening print preview with invalid printer.

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

Index: chrome/browser/ui/webui/print_preview/printer_capabilities.cc
diff --git a/chrome/browser/ui/webui/print_preview/printer_capabilities.cc b/chrome/browser/ui/webui/print_preview/printer_capabilities.cc
index 85cdf6764524eab50b527c8879809ba61627aa72..27c95fb8cf3f014f479de1a9c6a5a7c25b5dd945 100644
--- a/chrome/browser/ui/webui/print_preview/printer_capabilities.cc
+++ b/chrome/browser/ui/webui/print_preview/printer_capabilities.cc
@@ -25,7 +25,8 @@ const char kPrinterCapabilities[] = "capabilities";
 
 namespace {
 
-// Returns a Dictionary representing printer capabilities as CDD.
+// Returns a dictionary representing printer capabilities as CDD.  Returns
+// nullptr if a dictionary could not be generated.
 std::unique_ptr<base::DictionaryValue>
 GetPrinterCapabilitiesOnBlockingPoolThread(const std::string& device_name) {
   DCHECK(content::BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
@@ -94,8 +95,11 @@ std::unique_ptr<base::DictionaryValue> GetSettingsOnBlockingPool(
   printer_info->SetString(kSettingPrinterName, printer_name);
   printer_info->SetString(kSettingPrinterDescription, printer_description);
 
-  printer_info->Set(kPrinterCapabilities,
-                    GetPrinterCapabilitiesOnBlockingPoolThread(device_name));
+  std::unique_ptr<base::DictionaryValue> capabilities =
+      GetPrinterCapabilitiesOnBlockingPoolThread(device_name);
+  if (capabilities)
+    printer_info->Set(kPrinterCapabilities, std::move(capabilities));
+
   return printer_info;
 }