Fix Windows build, add Sandbox implementation.

webkit/child/BUILD.gn

 # Copyright 2014 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.
 
 component("child") {
   output_name = "webkit_child"
   sources = [
     "multipart_response_delegate.cc",
     "multipart_response_delegate.h",
     "resource_loader_bridge.cc",
     "resource_loader_bridge.h",
     "webkit_child_export.h",
     "weburlresponse_extradata_impl.cc",
     "weburlresponse_extradata_impl.h",
   ]
 
   defines = [ "WEBKIT_CHILD_IMPLEMENTATION" ]
   include_dirs = [
     # For JNI generated header.
     "$root_gen_dir/webkit",
   ]
 
   configs += [ "//build/config/compiler:wexit_time_destructors" ]
   if (is_win) {
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-    cflags += [ "/wd4267" ]
+    cflags = [ "/wd4267" ]
   }
 
   if (is_mac) {
     libs = [ "QuartzCore.framework" ]
   }
   if (is_android) {
     #deps += [ ":overscroller_jni_headers" ]  TODO(GYP)
   }
 
   deps = [
@@ skipping 14 matching lines @@
 
 #TODO(GYP)
 #'target_name': 'overscroller_jni_headers',
 #'type': 'none',
 #'variables': {
 #  'jni_gen_package': 'webkit',
 #  'input_java_class': 'android/widget/OverScroller.class',
 #},
 #'includes': [ '../../build/jar_file_jni_generator.gypi' ],