Make "remoting_core.*" optional until GYP issues (http://crbug.com/173052) are resolved.

chrome/tools/build/win/FILES.cfg

 # -*- python -*-
 # ex: set syntax=python:
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This is a buildbot configuration file containing a tagged list of files
 # processed by the stage/archive scripts. The known tags are:
 #
@@ skipping 360 matching lines @@
   {
     'filename': 'remoting_controller.exe.pdb',
     'buildtype': ['official'],
     'archive': 'remoting-win32.zip',
   },
   {
     'filename': 'remoting_core.dll',
     'buildtype': ['official'],
     'archive': 'remoting-win32.zip',
     'filegroup': ['symsrc'],
+    'optional': ['official'],
   },
   {
     'filename': 'remoting_core.dll.pdb',
     'buildtype': ['official'],
     'archive': 'remoting-win32.zip',
+    'optional': ['official'],
   },
   {
     'filename': 'remoting_desktop.exe',
     'buildtype': ['official'],
     'archive': 'remoting-win32.zip',
     'filegroup': ['symsrc'],
     'optional': ['official'],
   },
   {
     'filename': 'remoting_desktop.exe.pdb',
@@ skipping 265 matching lines @@
     'filename': 'syzygy/chrome.dll.pdb',
     'buildtype': ['official'],
     'archive': 'chrome-win32-syms.zip',
   },
   {
     'filename': 'syzygy/mini_installer.exe.pdb',
     'buildtype': ['official'],
     'archive': 'chrome-win32-syms.zip',
   },
 ]