Use absl::node_hash_map instead of std::unordered_map in QUICHE.

The plan here is to switch QUICHE to Abseil types in two steps:
  1) Change Chromium to use Abseil implementation of wrapper types.
  2) Replace wrapper types with Abseil types once chromium#1 lands.

This allows us to perform the switch without introducing churn caused by
having to roll back Abseil types in case those break something in Chromium.

Change-Id: I7efd58da2487c502aa03548901e370881de69a1f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410517
Commit-Queue: Victor Vasiliev <vasilvv@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: David Schinazi <dschinazi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806808}

net/quiche/common/platform/impl/DEPS

@@ -0,0 +1,6 @@
+include_rules = [
+  # This is a temporary rule to simplify migrating QUICHE to using Abseil
+  # directly.
+  # TODO(b/166325009): remove this rule.
+  "+third_party/abseil-cpp/absl/container/node_hash_map.h",
+]

net/quiche/common/platform/impl/quiche_unordered_containers_impl.h

@@ -7,20 +7,16 @@
 
 #include <unordered_map>
 
+#include "third_party/abseil-cpp/absl/container/node_hash_map.h"
+
 namespace quiche {
 
 // The default hasher used by hash tables.
 template <typename Key>
-using QuicheDefaultHasherImpl = std::hash<Key>;
-
-template <typename Key,
-          typename Value,
-          typename Hash,
-          typename Eq =
-              typename std::unordered_map<Key, Value, Hash>::key_equal,
-          typename Alloc =
-              typename std::unordered_map<Key, Value, Hash>::allocator_type>
-using QuicheUnorderedMapImpl = std::unordered_map<Key, Value, Hash, Eq, Alloc>;
+using QuicheDefaultHasherImpl = absl::Hash<Key>;
+
+template <typename Key, typename Value, typename Hash, typename Eq>
+using QuicheUnorderedMapImpl = absl::node_hash_map<Key, Value, Hash, Eq>;
 
 }  // namespace quiche