Format GN files and add a presubmit check that GN is properly formatted

utils/dartanalyzer/BUILD.gn

Index: utils/dartanalyzer/BUILD.gn
diff --git a/utils/dartanalyzer/BUILD.gn b/utils/dartanalyzer/BUILD.gn
index 91281680ac1bbf3d90ef8cda2d52301ea1bdc456..e4d4a6297f9e07a123e68ba187b59a6943f818b1 100644
--- a/utils/dartanalyzer/BUILD.gn
+++ b/utils/dartanalyzer/BUILD.gn
@@ -13,36 +13,36 @@ group("dartanalyzer") {
 }
 
 analyzer_files = exec_script("../../tools/list_dart_files.py",
-                             [rebase_path("../../pkg/analyzer")],
+                             [ rebase_path("../../pkg/analyzer") ],
                              "list lines")
 
 application_snapshot("generate_dartanalyzer_snapshot") {
   main_dart = "../../pkg/analyzer_cli/bin/analyzer.dart"
   training_args = [
     "--dart-sdk=" + rebase_path("../../sdk"),
-    rebase_path("../../tests/language/first_test.dart")
+    rebase_path("../../tests/language/first_test.dart"),
   ]
   name = "dartanalyzer"
   cli_files = exec_script("../../tools/list_dart_files.py",
-                          [rebase_path("../../pkg/analyzer_cli")],
+                          [ rebase_path("../../pkg/analyzer_cli") ],
                           "list lines")
   inputs = cli_files + analyzer_files
 }
 
 sdk_lib_files = exec_script("../../tools/list_dart_files.py",
-                            [rebase_path("../../sdk/lib")],
+                            [ rebase_path("../../sdk/lib") ],
                             "list lines")
 
 template("generate_summary") {
   assert(defined(invoker.type), "Must specify the summary type")
   type = invoker.type
-  assert((type == "spec") || (type == "strong"))
+  assert(type == "spec" || type == "strong")
   invoke_dart(target_name) {
     inputs = sdk_lib_files + analyzer_files
 
     output = "$root_gen_dir/$type.sum"
     outputs = [
-      output
+      output,
     ]
 
     dot_packages = rebase_path("../../.packages")