Fix crash on NULL pointer when the browser is compiled with use_cups=0

Please see https://bugs.gentoo.org/show_bug.cgi?id=530682 for context.

The idea is to make cups dependency optional at compile time. Even without
cups one can print to file (pdf) or use cloud print.

BUG=none
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/862023002

Cr-Commit-Position: refs/heads/master@{#312594}

2 files changed, 41 insertions, 3 deletions

diff --git a/printing/backend/print_backend.h b/printing/backend/print_backend.h
index e03ef42..a812332 100644
--- a/printing/backend/print_backend.h
+++ b/printing/backend/print_backend.h
@@ -111,7 +111,6 @@ class PRINTING_EXPORT PrintBackend
 
   // Allocate a print backend. If |print_backend_settings| is NULL, default
   // settings will be used.
-  // Return NULL if no print backend available.
   static scoped_refptr<PrintBackend> CreateInstance(
       const base::DictionaryValue* print_backend_settings);
 
diff --git a/printing/backend/print_backend_dummy.cc b/printing/backend/print_backend_dummy.cc
index c73e537..db269a7 100644
--- a/printing/backend/print_backend_dummy.cc
+++ b/printing/backend/print_backend_dummy.cc
@@ -13,10 +13,49 @@
 
 namespace printing {
 
+class DummyPrintBackend : public PrintBackend {
+ public:
+  DummyPrintBackend() {
+  }
+
+  bool EnumeratePrinters(PrinterList* printer_list) override {
+    return false;
+  }
+
+  std::string GetDefaultPrinterName() override {
+    return std::string();
+  }
+
+  bool GetPrinterSemanticCapsAndDefaults(
+      const std::string& printer_name,
+      PrinterSemanticCapsAndDefaults* printer_info) override {
+    return false;
+  }
+
+  bool GetPrinterCapsAndDefaults(
+      const std::string& printer_name,
+      PrinterCapsAndDefaults* printer_info) override {
+    return false;
+  }
+
+  std::string GetPrinterDriverInfo(
+      const std::string& printer_name) override {
+    return std::string();
+  }
+
+  bool IsValidPrinter(const std::string& printer_name) override {
+    return false;
+  }
+
+ private:
+  ~DummyPrintBackend() {}
+
+  DISALLOW_COPY_AND_ASSIGN(DummyPrintBackend);
+};
+
 scoped_refptr<PrintBackend> PrintBackend::CreateInstance(
     const base::DictionaryValue* print_backend_settings) {
-  NOTREACHED();
-  return NULL;
+  return new DummyPrintBackend();
 }
 
 }  // namespace printing