Add utils/unique_vector.h from TypeDeterminer

Add tests.

Change-Id: I064fbbe2387ebe980776ee99ed2ff48d6ea5d5b5
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/41621
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>
diff --git a/src/type_determiner.cc b/src/type_determiner.cc
index a72c3ab..3e0a797 100644
--- a/src/type_determiner.cc
+++ b/src/type_determiner.cc
@@ -125,9 +125,9 @@
     return;
   }
 
-  current_function_->referenced_module_vars.Add(var);
+  current_function_->referenced_module_vars.add(var);
   if (local) {
-    current_function_->local_referenced_module_vars.Add(var);
+    current_function_->local_referenced_module_vars.add(var);
   }
 }
 
@@ -172,7 +172,7 @@
 
 void TypeDeterminer::set_entry_points(const Symbol& fn_sym, Symbol ep_sym) {
   auto* info = symbol_to_function_.at(fn_sym);
-  info->ancestor_entry_points.Add(ep_sym);
+  info->ancestor_entry_points.add(ep_sym);
 
   for (const auto& callee : caller_to_callee_[fn_sym]) {
     set_entry_points(callee, ep_sym);