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

build/common.gypi

Index: build/common.gypi
===================================================================
--- build/common.gypi	(revision 266235)
+++ build/common.gypi	(working copy)
@@ -468,6 +468,9 @@
       # Enables used resource whitelist generation; disabled by default.
       'enable_resource_whitelist_generation%': 0,
 
+      # Enable FILE support by default.
+      'disable_file_support%': 0,
+
       # Enable FTP support by default.
       'disable_ftp_support%': 0,
 
@@ -1012,6 +1015,7 @@
     'cld2_table_size%': '<(cld2_table_size)',
     'cld2_dynamic%': '<(cld2_dynamic)',
     'enable_captive_portal_detection%': '<(enable_captive_portal_detection)',
+    'disable_file_support%': '<(disable_file_support)',
     'disable_ftp_support%': '<(disable_ftp_support)',
     'enable_task_manager%': '<(enable_task_manager)',
     'sas_dll_path%': '<(sas_dll_path)',
@@ -2561,6 +2565,9 @@
       ['enable_settings_app==1', {
         'defines': ['ENABLE_SETTINGS_APP=1'],
       }],
+      ['disable_file_support==1', {
+        'defines': ['DISABLE_FILE_SUPPORT=1'],
+      }],
       ['disable_ftp_support==1', {
         'defines': ['DISABLE_FTP_SUPPORT=1'],
       }],