Add GN option to disable js protobuf support.

This allows other projects like ANGLE to import protobuf and use the
GN files without importing the JS dependencies.

Bug: angleproject:5161
Change-Id: I71b08c7c03a63a186312edee0a4b55e95e75cf69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464426
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816251}

third_party/protobuf/BUILD.gn

@@ -3,7 +3,12 @@
 # found in the LICENSE file.
 import("//build/config/linux/gtk/gtk.gni")
 import("//build/config/sanitizers/sanitizers.gni")
-import("//third_party/closure_compiler/compile_js.gni")
+
+# Includes default args like 'enable_js_protobuf'.
+import("proto_library.gni")
+if (enable_js_protobuf) {
+  import("//third_party/closure_compiler/compile_js.gni")
+}
 
 config("protobuf_config") {
   include_dirs = [ "src" ]
@@ -225,10 +230,10 @@ static_library("protobuf_full") {
 
     # The protobuf-based SQLite and GPU fuzzers need protobuf_full and are not
     # included in Chrome.
-    "//third_party/sqlite:sqlite3_lpm_corpus_gen",
     "//gpu:gl_lpm_fuzzer_proto",
     "//gpu:gl_lpm_fuzzer_proto_gen",
     "//gpu:gl_lpm_shader_to_string_unittest",
+    "//third_party/sqlite:sqlite3_lpm_corpus_gen",
 
     # The protobuf-based Mojo LPM fuzzer needs protobuf_full and is not included
     # in Chrome.
@@ -680,7 +685,8 @@ group("py_proto_runtime") {
 }
 
 # JS protobuf library.
-js_library("js_proto") {
+if (enable_js_protobuf) {
+  js_library("js_proto") {
     sources = [
       "//third_party/google-closure-library/closure/goog/array/array.js",
       "//third_party/google-closure-library/closure/goog/asserts/asserts.js",
@@ -734,4 +740,5 @@ js_library("js_proto") {
       "js/map.js",
       "js/message.js",
     ]
+  }
 }

third_party/protobuf/proto_library.gni

@@ -120,7 +120,16 @@
 
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/kythe.gni")
-import("//third_party/closure_compiler/compile_js.gni")
+
+declare_args() {
+  # Allows subprojects to omit javascript dependencies (e.g.) closure_compiler
+  # and google-closure-library.
+  enable_js_protobuf = true
+}
+
+if (enable_js_protobuf) {
+  import("//third_party/closure_compiler/compile_js.gni")
+}
 
 if (host_os == "win") {
   _host_executable_suffix = ".exe"