Revert "Replace use of std containers with WTF's equivalents in html_slot_element.h"

This reverts commit c2d3f186.

Reason for revert: Suspecting this CL for test failures in Linux CFI
https://ci.chromium.org/p/chromium/builders/ci/Linux%20CFI

See first test failure of AdsPageLoadMetricsObserverResourceBrowserTest.AdFrameSizeInterventionMediaStatusPlayed here:
https://ci.chromium.org/p/chromium/builders/ci/Linux%20CFI/14253

Suspecting this CL since it was the only one that touched code in t/p/b/r/c/html for that blamelist and crash shows blink::HTMLParserScheduler::ScheduleForUnpause within stack trace.

Original change's description:
> Replace use of std containers with WTF's equivalents in html_slot_element.h
> 
> This CL replaces the use of std::array of std containers with WTF::Vector
> and introduces LCSArray struct in html_slot_element.h.
> 
> Bug: 952716
> Change-Id: I45d0dcbb63aed5198440bd7b94c5c693a05bd6fd
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1694801
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
> Cr-Commit-Position: refs/heads/master@{#675985}

TBR=haraken@chromium.org,myid.shin@igalia.com

Change-Id: Ibf0a3bb5b4d4f579085986b941a5d6e710d0e6fc
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 952716
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696007Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676073}

third_party/blink/renderer/core/html/html_slot_element.cc

@@ -30,6 +30,8 @@
 
 #include "third_party/blink/renderer/core/html/html_slot_element.h"
 
+#include <array>
+
 #include "third_party/blink/renderer/core/css/style_change_reason.h"
 #include "third_party/blink/renderer/core/css/style_engine.h"
 #include "third_party/blink/renderer/core/dom/events/event.h"
@@ -397,15 +399,14 @@ void HTMLSlotElement::NotifySlottedNodesOfFlatTreeChangeByDynamicProgramming(
     const HeapVector<Member<Node>>& old_slotted,
     const HeapVector<Member<Node>>& new_slotted) {
   // Use dynamic programming to minimize the number of nodes being reattached.
-  using LCSTable =
-      Vector<LCSArray<wtf_size_t, kLCSTableSizeLimit>, kLCSTableSizeLimit>;
+  using LCSTable = std::array<std::array<wtf_size_t, kLCSTableSizeLimit>,
+                              kLCSTableSizeLimit>;
   using Backtrack = std::pair<wtf_size_t, wtf_size_t>;
   using BacktrackTable =
-      Vector<LCSArray<Backtrack, kLCSTableSizeLimit>, kLCSTableSizeLimit>;
+      std::array<std::array<Backtrack, kLCSTableSizeLimit>, kLCSTableSizeLimit>;
 
-  DEFINE_STATIC_LOCAL(LCSTable*, lcs_table, (new LCSTable(kLCSTableSizeLimit)));
-  DEFINE_STATIC_LOCAL(BacktrackTable*, backtrack_table,
-                      (new BacktrackTable(kLCSTableSizeLimit)));
+  DEFINE_STATIC_LOCAL(LCSTable*, lcs_table, (new LCSTable));
+  DEFINE_STATIC_LOCAL(BacktrackTable*, backtrack_table, (new BacktrackTable));
 
   FillLongestCommonSubsequenceDynamicProgrammingTable(
       old_slotted, new_slotted, *lcs_table, *backtrack_table);

third_party/blink/renderer/core/html/html_slot_element.h

@@ -148,14 +148,6 @@ class CORE_EXPORT HTMLSlotElement final : public HTMLElement {
   // For imperative Shadow DOM distribution APIs
   HeapHashSet<Member<Node>> assigned_nodes_candidates_;
 
-  template <typename T, wtf_size_t S>
-  struct LCSArray {
-    LCSArray() : values(S) {}
-    T& operator[](wtf_size_t i) { return values[i]; }
-    wtf_size_t size() { return values.size(); }
-    Vector<T, S> values;
-  };
-
   // TODO(hayato): Move this to more appropriate directory (e.g. platform/wtf)
   // if there are more than one usages.
   template <typename Container, typename LCSTable, typename BacktrackTable>

third_party/blink/renderer/core/html/html_slot_element_test.cc

@@ -4,6 +4,8 @@
 
 #include "third_party/blink/renderer/core/html/html_slot_element.h"
 
+#include <array>
+
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/blink/renderer/core/css/style_engine.h"
 #include "third_party/blink/renderer/core/dom/node_computed_style.h"
@@ -20,12 +22,10 @@ using Backtrack = std::pair<size_t, size_t>;
 
 class HTMLSlotElementTest : public testing::Test {
  protected:
-  HTMLSlotElementTest()
-      : lcs_table_(kTableSize), backtrack_table_(kTableSize) {}
+  HTMLSlotElementTest() = default;
   Seq LongestCommonSubsequence(const Seq& seq1, const Seq& seq2);
-  Vector<HTMLSlotElement::LCSArray<size_t, kTableSize>, kTableSize> lcs_table_;
-  Vector<HTMLSlotElement::LCSArray<Backtrack, kTableSize>, kTableSize>
-      backtrack_table_;
+  std::array<std::array<size_t, kTableSize>, kTableSize> lcs_table_;
+  std::array<std::array<Backtrack, kTableSize>, kTableSize> backtrack_table_;
 };
 
 Vector<char> HTMLSlotElementTest::LongestCommonSubsequence(const Seq& seq1,