Unpoinson CrossThreadWeakPersistents in ThreadHeap::PoisonAllHeaps

ThreadHeap::PoisonAllHeaps was not CrossThreadWeakPersistents which was causing ASAN crashes

Fixes mistake made in r425667

Bug: 986751
Change-Id: I4ce5750970388dba8983fc8cee8c2386acb1e61d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1722979Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681692}

third_party/blink/renderer/platform/heap/heap.cc

@@ -509,6 +509,8 @@ void ThreadHeap::PoisonAllHeaps() {
   // that would be fine.
   ProcessHeap::GetCrossThreadPersistentRegion()
       .UnpoisonCrossThreadPersistents();
+  ProcessHeap::GetCrossThreadWeakPersistentRegion()
+      .UnpoisonCrossThreadPersistents();
 }
 #endif