Use extension-based file picker from CrOS for Aura builds.

chrome/browser/extensions/extension_file_browser_private_api.h

Index: chrome/browser/extensions/extension_file_browser_private_api.h
diff --git a/chrome/browser/extensions/extension_file_browser_private_api.h b/chrome/browser/extensions/extension_file_browser_private_api.h
index 7c7716dfe228003d9691b9a592efbad1cfe152a9..3b3602ee51399f12be0b82b2e068630f6935ce4c 100644
--- a/chrome/browser/extensions/extension_file_browser_private_api.h
+++ b/chrome/browser/extensions/extension_file_browser_private_api.h
@@ -233,6 +233,7 @@ class AddMountFunction
                                                void* context) OVERRIDE;
 
  private:
+#if defined(OS_CHROMEOS)
   struct MountParamaters {
     MountParamaters(const std::string& type,
                     const chromeos::MountPathOptions& options)
@@ -241,6 +242,7 @@ class AddMountFunction
     std::string mount_type;
     chromeos::MountPathOptions mount_options;
   };
+#endif
 
   DECLARE_EXTENSION_FUNCTION_NAME("fileBrowserPrivate.addMount");
 };
@@ -308,7 +310,7 @@ class GetVolumeMetadataFunction
   virtual bool RunImpl() OVERRIDE;
 
  private:
-#ifdef OS_CHROMEOS
+#if defined(OS_CHROMEOS)
   const std::string& DeviceTypeToString(chromeos::DeviceType type);
 #endif