Validate GN substitutions in args and rsp files.

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 c6ea38597dd44c2118e9f5aa45bbc2e382b933eb..99b4e6802df7b49a250dffd4e812878b3ba69b6d 100644
--- a/tools/gn/substitution_type.cc
+++ b/tools/gn/substitution_type.cc
@@ -166,6 +166,11 @@ bool IsValidSourceSubstitution(SubstitutionType type) {
          type == SUBSTITUTION_SOURCE_TARGET_RELATIVE;
 }
 
+bool IsValidScriptArgsSubstitution(SubstitutionType type) {
+  return IsValidSourceSubstitution(type) ||
+      type == SUBSTITUTION_RSP_FILE_NAME;
+}
+
 bool IsValidToolSubstitution(SubstitutionType type) {
   return type == SUBSTITUTION_LITERAL ||
          type == SUBSTITUTION_OUTPUT ||
@@ -236,14 +241,14 @@ bool IsValidCompileXCassetsSubstitution(SubstitutionType type) {
          type == SUBSTITUTION_BUNDLE_PRODUCT_TYPE;
 }
 
-bool EnsureValidSourcesSubstitutions(
-    const std::vector<SubstitutionType>& types,
-    const ParseNode* origin,
-    Err* err) {
-  for (size_t i = 0; i < types.size(); i++) {
-    if (!IsValidSourceSubstitution(types[i])) {
+bool EnsureValidSubstitutions(const std::vector<SubstitutionType>& types,
+                              bool (*is_valid_subst)(SubstitutionType),
+                              const ParseNode* origin,
+                              Err* err) {
+  for (SubstitutionType type : types) {
+    if (!is_valid_subst(type)) {
       *err = Err(origin, "Invalid substitution type.",
-          "The substitution " + std::string(kSubstitutionNames[types[i]]) +
+          "The substitution " + std::string(kSubstitutionNames[type]) +
           " isn't valid for something\n"
           "operating on a source file such as this.");
       return false;