[LTS-M86][builtins] Harden Array.prototype.concat.

Defence in depth patch to prevent JavaScript from executing
from within IterateElements.

R=​ishell@chromium.org
R=​cbruni@chromium.org

(cherry picked from commit 8284359)

No-Try: true
No-Presubmit: true
No-Tree-Checks: true
Bug: chromium:1195977
Change-Id: Ie59d468b73b94818cea986a3ded0804f6dddd10b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2819941
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#73898}
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2821961
Commit-Queue: Jana Grill <janagrill@chromium.org>
Reviewed-by: Victor-Gabriel Savu <vsavu@google.com>
Cr-Commit-Position: refs/branch-heads/8.6@{#76}
Cr-Branched-From: a64aed2-refs/heads/8.6.395@{#1}
Cr-Branched-From: a626bc0-refs/heads/master@{#69472}

AUTHORS

@@ -67,6 +67,7 @@ Ben Newman <ben@meteor.com>
 Ben Noordhuis <info@bnoordhuis.nl>
 Benjamin Tan <demoneaux@gmail.com>
 Bert Belder <bertbelder@gmail.com>
+Brendon Tiszka <btiszka@gmail.com>
 Burcu Dogan <burcujdogan@gmail.com>
 Caitlin Potter <caitpotter88@gmail.com>
 Craig Schlenter <craig.schlenter@gmail.com>

src/builtins/builtins-array.cc

@@ -1080,6 +1080,9 @@ bool IterateElements(Isolate* isolate, Handle<JSReceiver> receiver,
     case HOLEY_SEALED_ELEMENTS:
     case HOLEY_NONEXTENSIBLE_ELEMENTS:
     case HOLEY_ELEMENTS: {
+      // Disallow execution so the cached elements won't change mid execution.
+      DisallowJavascriptExecution no_js(isolate);
+
       // Run through the elements FixedArray and use HasElement and GetElement
       // to check the prototype for missing elements.
       Handle<FixedArray> elements(FixedArray::cast(array->elements()), isolate);
@@ -1106,6 +1109,9 @@ bool IterateElements(Isolate* isolate, Handle<JSReceiver> receiver,
     }
     case HOLEY_DOUBLE_ELEMENTS:
     case PACKED_DOUBLE_ELEMENTS: {
+      // Disallow execution so the cached elements won't change mid execution.
+      DisallowJavascriptExecution no_js(isolate);
+
       // Empty array is FixedArray but not FixedDoubleArray.
       if (length == 0) break;
       // Run through the elements FixedArray and use HasElement and GetElement
@@ -1142,6 +1148,9 @@ bool IterateElements(Isolate* isolate, Handle<JSReceiver> receiver,
     }
 
     case DICTIONARY_ELEMENTS: {
+      // Disallow execution so the cached dictionary won't change mid execution.
+      DisallowJavascriptExecution no_js(isolate);
+
       Handle<NumberDictionary> dict(array->element_dictionary(), isolate);
       std::vector<uint32_t> indices;
       indices.reserve(dict->Capacity() / 2);