Port most sync targets to sync/BUILD.gn

BUILD.gn

 # Copyright (c) 2013 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 the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 40 matching lines @@
     "//media/cast",
     "//mojo",
     "//net",
     "//pdf",
     "//ppapi:ppapi_c",
     "//printing",
     "//sandbox",
     "//sdch",
     "//skia",
     "//sql",
+    "//sync",
     "//third_party/WebKit/public:all_blink",
     "//third_party/angle:translator",
     "//third_party/brotli",
     "//third_party/cacheinvalidation",
     "//third_party/cld",
     "//third_party/cld_2",
     "//third_party/ffmpeg",
     "//third_party/flac",
     "//third_party/harfbuzz-ng",
     "//third_party/hunspell",
@@ skipping 145 matching lines @@
     ]
   }
 
   if (use_ozone) {
     deps += [
       "//ui/ozone",
       "//ui/ozone/demo",
     ]
   }
 }