Add ContainsKey() and ContainsValue() and use them where appropriate.

third_party/base/stl_util.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PDFIUM_THIRD_PARTY_BASE_STL_UTIL_H_
 #define PDFIUM_THIRD_PARTY_BASE_STL_UTIL_H_
 
 #include <vector>
 
 namespace pdfium {
 
 // To treat a possibly-empty vector as an array, use these functions.
 // If you know the array will never be empty, you can use &*v.begin()
 // directly, but that is undefined behaviour if |v| is empty.
 template <typename T>
 inline T* vector_as_array(std::vector<T>* v) {
   return v->empty() ? nullptr : &*v->begin();
 }
 
 template <typename T>
 inline const T* vector_as_array(const std::vector<T>* v) {
   return v->empty() ? nullptr : &*v->begin();
 }
 
+// Test to see if a set, map, hash_set or hash_map contains a particular key.
+// Returns true if the key is in the collection.
+template <typename Collection, typename Key>
+bool ContainsKey(const Collection& collection, const Key& key) {
+  return collection.find(key) != collection.end();
+}
+
+// Test to see if a collection like a vector contains a particular value.
+// Returns true if the value is in the collection.
+template <typename Collection, typename Value>
+bool ContainsValue(const Collection& collection, const Value& value) {
+  return std::find(collection.begin(), collection.end(), value) !=
+         collection.end();
+}
+
 }  // namespace pdfium
 
 #endif  // PDFIUM_THIRD_PARTY_BASE_STL_UTIL_H_