Gets gn check to execute cleanly in mojo/common

.gn

 # This file is used by the GN meta build system to find the root of the source
 # tree and to set startup options. For documentation on the values set in this
 # file, run "gn help dotfile" at the command line.
 
 # The location of the build configuration file.
 buildconfig = "//build/config/BUILDCONFIG.gn"
 
 # The secondary source root is a parallel directory tree where
 # GN build files are placed when they can not be placed directly
 # in the source tree, e.g. for third party source trees.
@@ skipping 57 matching lines @@
 
   #"//ios/*",
   "//ipc/*",
 
   #"//jingle/*",
   #"//media/*",  # Lots of errors.
   "mojo/android/*",
   "mojo/application/*",
   "mojo/build/*",
   "mojo/cc/*",
-
-  # TODO(sky): resolve this.
-  # "mojo/common/*",
+  "mojo/common/*",
   "mojo/converters/*",
   "mojo/environment/*",
 
   # TODO(sky): resolve this.
   # "mojo/gles2/*",
   "mojo/gpu/*",
   "mojo/nacl/*",
 
   # TODO(sky): resolve this.
   # "mojo/platform_handle/*",
@@ skipping 139 matching lines @@
   "//tools/gn/format_test_data/055.golden",
   "//tools/gn/function_exec_script.cc",
   "//tools/gn/gn.gyp",
   "//tools/gn/input_conversion.cc",
   "//tools/gn/misc/emacs/gn.el",
   "//tools/gn/misc/vim/syntax/gn.vim",
   "//tools/gn/setup.cc",
   "//ui/accessibility/BUILD.gn",
   "//ui/views/BUILD.gn",
 ]