Add an assert_no_deps variable to GN.

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 3734ea9c3424ccf82c7511268a6438b07d9ac259..b1ed1ea3e3bcdfb1a49768580264d7ec67159b35 100644
--- a/tools/gn/target_generator.cc
+++ b/tools/gn/target_generator.cc
@@ -50,6 +50,9 @@ void TargetGenerator::Run() {
   if (!FillTestonly())
     return;
 
+  if (!FillAssertNoDeps())
+    return;
+
   if (!Visibility::FillItemVisibility(target_, scope_, err_))
     return;
 
@@ -266,6 +269,15 @@ bool TargetGenerator::FillTestonly() {
   return true;
 }
 
+bool TargetGenerator::FillAssertNoDeps() {
+  const Value* value = scope_->GetValue(variables::kAssertNoDeps, true);
+  if (value) {
+    return ExtractListOfLabelPatterns(*value, scope_->GetSourceDir(),
+                                      &target_->assert_no_deps(), err_);
+  }
+  return true;
+}
+
 bool TargetGenerator::FillOutputs(bool allow_substitutions) {
   const Value* value = scope_->GetValue(variables::kOutputs, true);
   if (!value)