Avoid a use-after-move in `QuicheLinkedHashMap::TryEmplaceInternal`.

When `key` is a rvalue, `QuicheLinkedHashMap::TryEmplaceInternal` currently moves it twice:
- First time into the map: `map_.try_emplace(std::forward<K>(key))`
- Second time into the list: `std::forward_as_tuple(std::forward<K>(key))`

This will cause the key in the list to be in the moved-from state => BUG.

The fix is to replace the second move by a copy.

PiperOrigin-RevId: 965986514

quiche/common/quiche_linked_hash_map.h

diff --git a/quiche/common/quiche_linked_hash_map.h b/quiche/common/quiche_linked_hash_map.h
index 3932844..4d4e630 100644
--- a/quiche/common/quiche_linked_hash_map.h
+++ b/quiche/common/quiche_linked_hash_map.h
@@ -231,7 +231,7 @@
 
     auto list_iter =
         list_.emplace(list_.end(), std::piecewise_construct,
-                      std::forward_as_tuple(std::forward<K>(key)),
+                      std::forward_as_tuple(insert_result.first->first),
                       std::forward_as_tuple(std::forward<Args>(args)...));
 
     insert_result.first->second = list_iter;

quiche/common/quiche_linked_hash_map_test.cc

diff --git a/quiche/common/quiche_linked_hash_map_test.cc b/quiche/common/quiche_linked_hash_map_test.cc
index 98a731a..4bdb23e 100644
--- a/quiche/common/quiche_linked_hash_map_test.cc
+++ b/quiche/common/quiche_linked_hash_map_test.cc
@@ -7,6 +7,7 @@
 #include "quiche/common/quiche_linked_hash_map.h"
 
 #include <memory>
+#include <string>
 #include <tuple>
 #include <utility>
 
@@ -69,6 +70,16 @@
   EXPECT_EQ(234, found->second.x);
 }
 
+TEST(LinkedHashMapTest, TryEmplaceRvalueKey) {
+  QuicheLinkedHashMap<std::string, int> m;
+  std::string key = "hello";
+  auto result = m.try_emplace(std::move(key), 42);
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(result.first->first, "hello");
+  EXPECT_EQ(m.find("hello")->first, "hello");
+  EXPECT_EQ(m.begin()->first, "hello");
+}
+
 TEST(LinkedHashMapTest, ConstKeys) {
   QuicheLinkedHashMap<int, int> m;
   m.insert(std::make_pair(1, 2));