Add GN buildfiles for ui/compositor and snapshot.

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 56 matching lines @@
     "//third_party/smhasher:murmurhash3",
     "//third_party/smhasher:pmurhash",
     # TODO(brettw) re-enable once the unused variables in this .gn file are
     # fixed and rolled into Chrome.
     #"//third_party/WebKit/Source/platform",
     "//third_party/WebKit/Source/wtf",
     "//third_party/zlib",
     "//third_party:jpeg",
     "//tools/gn",
     "//ui/accessibility",
-    "//ui/base:ui_base",
+    "//ui/base",
     "//ui/events",
     "//ui/gfx",
     "//ui/gl",
     "//ui/native_theme",
     "//ui/resources",
+    "//ui/snapshot",
     "//ui/strings",
     "//ui/surface",
     "//url",
     "//v8:mksnapshot",
   ]
 
   if (is_linux) {
     deps += [
       "//third_party/freetype2",
     ]
@@ skipping 13 matching lines @@
       "//ppapi:ppapi_c",
       "//third_party/libusb",
       #"//third_party/WebKit/Source/platform",
       "//third_party/WebKit/Source/wtf",  # TODO(brettw) re-enable for Android.
       "//tools/gn",
 
       # This stuff all depends on ui/surface which requires some .class jni
       # generators (ui/gl/gl.gyp:surface_jni_headers).
       "//ui/gl",
       "//gpu",
+      "//ui/snapshot",
       "//ui/surface",
     ]
   }
 }