Add arflags to GN

tools/gn/substitution_type.cc

Index: tools/gn/substitution_type.cc
diff --git a/tools/gn/substitution_type.cc b/tools/gn/substitution_type.cc
index 75d8b7a80ddb2c8fea87eb4d5b8d52398a4ac56f..fcca19dac06cad952d2c375f7a8dde6df4a372b7 100644
--- a/tools/gn/substitution_type.cc
+++ b/tools/gn/substitution_type.cc
@@ -47,6 +47,8 @@ const char* kSubstitutionNames[SUBSTITUTION_NUM_TYPES] = {
   "{{output_extension}}",  // SUBSTITUTION_OUTPUT_EXTENSION
   "{{solibs}}",  // SUBSTITUTION_SOLIBS
 
+  "{{arflags}}",  // SUBSTITUTION_ARFLAGS
+
   "{{bundle_root_dir}}",  // SUBSTITUTION_BUNDLE_ROOT_DIR
   "{{bundle_resources_dir}}",  // SUBSTITUTION_BUNDLE_RESOURCES_DIR
   "{{bundle_executable_dir}}",  // SUBSTITUTION_BUNDLE_EXECUTABLE_DIR
@@ -96,6 +98,8 @@ const char* kSubstitutionNinjaNames[SUBSTITUTION_NUM_TYPES] = {
     "output_extension",  // SUBSTITUTION_OUTPUT_EXTENSION
     "solibs",            // SUBSTITUTION_SOLIBS
 
+    "arflags",           // SUBSTITUTION_ARFLAGS
+
     "bundle_root_dir",        // SUBSTITUTION_BUNDLE_ROOT_DIR
     "bundle_resources_dir",   // SUBSTITUTION_BUNDLE_RESOURCES_DIR
     "bundle_executable_dir",  // SUBSTITUTION_BUNDLE_EXECUTABLE_DIR
@@ -207,6 +211,15 @@ bool IsValidLinkerOutputsSubstitution(SubstitutionType type) {
          type == SUBSTITUTION_OUTPUT_EXTENSION;
 }
 
+bool IsValidALinkSubstitution(SubstitutionType type) {
+  return IsValidToolSubstitution(type) ||
+         type == SUBSTITUTION_LINKER_INPUTS ||
+         type == SUBSTITUTION_LINKER_INPUTS_NEWLINE ||
+         type == SUBSTITUTION_ARFLAGS ||
+         type == SUBSTITUTION_OUTPUT_DIR ||
+         type == SUBSTITUTION_OUTPUT_EXTENSION;
+}
+
 bool IsValidCopySubstitution(SubstitutionType type) {
   return IsValidToolSubstitution(type) ||
          type == SUBSTITUTION_SOURCE;