Satisfy gn check. (google#591)

Fix issues found by gn check and gn format.
Remove files that don't exist and add files libshaderc_spvc depends on.

BUILD.gn

@@ -1,11 +1,11 @@
 # Copyright 2018 The Shaderc Authors. All rights reserved.
-# 
+#
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
-# 
+#
 # http://www.apache.org/licenses/LICENSE-2.0
-# 
+#
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -24,7 +24,6 @@ config("shaderc_util_public") {
 
 source_set("shaderc_util_sources") {
  sources = [
- "libshaderc_util/include/libshaderc_util/common.h",
  "libshaderc_util/include/libshaderc_util/counting_includer.h",
  "libshaderc_util/include/libshaderc_util/exceptions.h",
  "libshaderc_util/include/libshaderc_util/file_finder.h",
@@ -37,7 +36,6 @@ source_set("shaderc_util_sources") {
  "libshaderc_util/include/libshaderc_util/string_piece.h",
  "libshaderc_util/include/libshaderc_util/universal_unistd.h",
  "libshaderc_util/include/libshaderc_util/version_profile.h",
- "libshaderc_util/include/libshaderc_util/visibility.h",
  "libshaderc_util/src/compiler.cc",
  "libshaderc_util/src/file_finder.cc",
  "libshaderc_util/src/io.cc",
@@ -111,12 +109,15 @@ component("libshaderc_spvc") {
  defines = [ "SHADERC_IMPLEMENTATION" ]
 
  sources = [
+ "libshaderc/include/shaderc/env.h",
+ "libshaderc/include/shaderc/status.h",
+ "libshaderc/include/shaderc/visibility.h",
  "libshaderc_spvc/include/shaderc/spvc.h",
  "libshaderc_spvc/include/shaderc/spvc.hpp",
  "libshaderc_spvc/src/spvc.cc",
  ]
 
- deps = [
+  deps = [
  ":shaderc_util_sources",
  "${spirv_tools_dir}:spvtools",
  "${spirv_tools_dir}:spvtools_val",