Make it so net/ can be built without file:// support.

net/url_request/url_request_context_builder.h

Index: net/url_request/url_request_context_builder.h
===================================================================
--- net/url_request/url_request_context_builder.h	(revision 268640)
+++ net/url_request/url_request_context_builder.h	(working copy)
@@ -89,10 +89,12 @@
     data_enabled_ = enable;
   }
 
+#if !defined(DISABLE_FILE_SUPPORT)
   // Control support for file:// requests. By default it's disabled.
   void set_file_enabled(bool enable) {
     file_enabled_ = enable;
   }
+#endif
 
 #if !defined(DISABLE_FTP_SUPPORT)
   // Control support for ftp:// requests. By default it's disabled.
@@ -157,8 +159,10 @@
   std::string user_agent_;
   // Include support for data:// requests.
   bool data_enabled_;
+#if !defined(DISABLE_FILE_SUPPORT)
   // Include support for file:// requests.
   bool file_enabled_;
+#endif
 #if !defined(DISABLE_FTP_SUPPORT)
   // Include support for ftp:// requests.
   bool ftp_enabled_;