Add //ipc to "gn check", work on base

.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.
 secondary_source = "//build/secondary/"
 
 # These are the targets to check headers for by default. The files in targets
 # matching these patterns (see "gn help label_pattern" for format) will have
 # their includes checked for proper dependencies when you run either
 # "gn check" or "gn gen --check".
-check_targets = [ "//cc/*" ]
+check_targets = [
+  # Requires GN binary >= 314794 and to mark the "...__generate_enum" action in
+  # build/config/android/rules.gni "java_cpp_enum" template with
+  #   check_includes = false.
+  #"//base/*",
+  "//cc/*",
+  "//ipc/*",
+]