Oilpan: Clear all Persistents on thread termination.

Persistents should be cleared when NumberOfPersistents() != 0.

Bug: 831117
Change-Id: Ie6209d822c1d14a79936cb2807f1da7e559a42b2
Reviewed-on: https://chromium-review.googlesource.com/1089460
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Lucas Gadani <lfg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565144}

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

@@ -249,7 +249,7 @@ void ThreadState::RunTerminationGC() {
   // if we have it is a bug, and we have a reference cycle or a missing
   // RegisterAsStaticReference. Clearing out all the Persistents will avoid
   // stale pointers and gets them reported as nullptr dereferences.
-  if (!current_count) {
+  if (current_count) {
     for (size_t i = 0; i < kMaxTerminationGCLoops &&
                        GetPersistentRegion()->NumberOfPersistents();
          i++) {
@@ -259,7 +259,7 @@ void ThreadState::RunTerminationGC() {
     }
   }
 
-  DCHECK(!GetPersistentRegion()->NumberOfPersistents());
+  CHECK(!GetPersistentRegion()->NumberOfPersistents());
 
   // All of pre-finalizers should be consumed.
   DCHECK(ordered_pre_finalizers_.IsEmpty());