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>

src/utils/unique_vector.h

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+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_UTILS_UNIQUE_VECTOR_H_
+#define SRC_UTILS_UNIQUE_VECTOR_H_
+
+#include <unordered_set>
+#include <vector>
+
+namespace tint {
+
+/// UniqueVector is an ordered container that only contains unique items.
+/// Attempting to add a duplicate is a no-op.
+template <typename T>
+struct UniqueVector {
+  /// The iterator returned by begin() and end()
+  using ConstIterator = typename std::vector<T>::const_iterator;
+
+  /// add appends the item to the end of the vector, if the vector does not
+  /// already contain the given item.
+  /// @param item the item to append to the end of the vector
+  void add(const T& item) {
+    if (set.count(item) == 0) {
+      vector.emplace_back(item);
+      set.emplace(item);
+    }
+  }
+
+  /// @returns the number of items in the vector
+  size_t size() const { return vector.size(); }
+
+  /// @returns an iterator to the beginning of the vector
+  ConstIterator begin() const { return vector.begin(); }
+
+  /// @returns an iterator to the end of the vector
+  ConstIterator end() const { return vector.end(); }
+
+  /// @returns a const reference to the internal vector
+  operator const std::vector<T> &() const { return vector; }
+
+ private:
+  std::vector<T> vector;
+  std::unordered_set<T> set;
+};
+
+}  // namespace tint
+
+#endif  //  SRC_UTILS_UNIQUE_VECTOR_H_

src/utils/unique_vector_test.cc

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+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/utils/unique_vector.h"
+
+#include "gtest/gtest.h"
+
+namespace tint {
+namespace {
+
+TEST(UniqueVectorTest, Empty) {
+  UniqueVector<int> unique_vec;
+  EXPECT_EQ(unique_vec.size(), 0u);
+  EXPECT_EQ(unique_vec.begin(), unique_vec.end());
+}
+
+TEST(UniqueVectorTest, AddUnique) {
+  UniqueVector<int> unique_vec;
+  unique_vec.add(0);
+  unique_vec.add(1);
+  unique_vec.add(2);
+  EXPECT_EQ(unique_vec.size(), 3u);
+  int i = 0;
+  for (auto n : unique_vec) {
+    EXPECT_EQ(n, i);
+    i++;
+  }
+}
+
+TEST(UniqueVectorTest, AddDuplicates) {
+  UniqueVector<int> unique_vec;
+  unique_vec.add(0);
+  unique_vec.add(0);
+  unique_vec.add(0);
+  unique_vec.add(1);
+  unique_vec.add(1);
+  unique_vec.add(2);
+  EXPECT_EQ(unique_vec.size(), 3u);
+  int i = 0;
+  for (auto n : unique_vec) {
+    EXPECT_EQ(n, i);
+    i++;
+  }
+}
+
+TEST(UniqueVectorTest, AsVector) {
+  UniqueVector<int> unique_vec;
+  unique_vec.add(0);
+  unique_vec.add(0);
+  unique_vec.add(0);
+  unique_vec.add(1);
+  unique_vec.add(1);
+  unique_vec.add(2);
+
+  const std::vector<int>& vec = unique_vec;
+  EXPECT_EQ(vec.size(), 3u);
+  int i = 0;
+  for (auto n : vec) {
+    EXPECT_EQ(n, i);
+    i++;
+  }
+}
+
+}  // namespace
+}  // namespace tint