Convert enable_pre_sync_backup flag to new flags system.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 54219d004628885a1be0b1f4774139125e15f0bf..b8e2a4408759c17b24842b953de9c25f9a7d1455 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -549,9 +549,6 @@
       # Whether one-click signin is enabled or not.
       'enable_one_click_signin%': 0,
 
-      # Whether to back up data before sync.
-      'enable_pre_sync_backup%': 0,
-
       # Enable Chrome browser extensions
       'enable_extensions%': 1,
 
@@ -814,7 +811,6 @@
 
         ['OS=="win" or OS=="mac" or (OS=="linux" and chromeos==0)', {
           'enable_one_click_signin%': 1,
-          'enable_pre_sync_backup%': 1,
         }],
 
         ['OS=="android"', {
@@ -1165,7 +1161,6 @@
     'use_titlecase_in_grd%': '<(use_titlecase_in_grd)',
     'remoting%': '<(remoting)',
     'enable_one_click_signin%': '<(enable_one_click_signin)',
-    'enable_pre_sync_backup%': '<(enable_pre_sync_backup)',
     'enable_media_router%': '<(enable_media_router)',
     'enable_webrtc%': '<(enable_webrtc)',
     'chromium_win_pch%': '<(chromium_win_pch)',
@@ -2721,9 +2716,6 @@
       ['enable_one_click_signin==1', {
         'defines': ['ENABLE_ONE_CLICK_SIGNIN'],
       }],
-      ['enable_pre_sync_backup==1', {
-        'defines': ['ENABLE_PRE_SYNC_BACKUP'],
-      }],
       ['image_loader_extension==1', {
         'defines': ['IMAGE_LOADER_EXTENSION=1'],
       }],