gn: Allow users to set 'check_includes' in action_foreach().

tools/gn/target_generator.cc

Index: tools/gn/target_generator.cc
diff --git a/tools/gn/target_generator.cc b/tools/gn/target_generator.cc
index db7befcab947fb6e3758c6f9b9e97e8ba93c8db8..797ffaa4e4bc984426312af54387f2c391f11e11 100644
--- a/tools/gn/target_generator.cc
+++ b/tools/gn/target_generator.cc
@@ -283,6 +283,16 @@ bool TargetGenerator::FillOutputs(bool allow_substitutions) {
   return true;
 }
 
+bool TargetGenerator::FillCheckIncludes() {
+  const Value* value = scope_->GetValue(variables::kCheckIncludes, true);
+  if (!value)
+    return true;
+  if (!value->VerifyTypeIs(Value::BOOLEAN, err_))
+    return false;
+  target_->set_check_includes(value->boolean_value());
+  return true;
+}
+
 bool TargetGenerator::EnsureSubstitutionIsInOutputDir(
     const SubstitutionPattern& pattern,
     const Value& original_value) {