[heap] Tests can now set FLAG_local_heaps from the get-go

Bug: v8:10315
Change-Id: I0144b89696933afcd02f63b0440118dd33a7d5ad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2225025Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68127}

test/cctest/heap/test-concurrent-allocation.cc

@@ -74,14 +74,13 @@ class ConcurrentAllocationThread final : public v8::base::Thread {
 UNINITIALIZED_TEST(ConcurrentAllocationInOldSpace) {
   FLAG_max_old_space_size = 32;
   FLAG_concurrent_allocation = true;
+  FLAG_local_heaps = true;
 
   v8::Isolate::CreateParams create_params;
   create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
   v8::Isolate* isolate = v8::Isolate::New(create_params);
   Isolate* i_isolate = reinterpret_cast<Isolate*>(isolate);
 
-  FLAG_local_heaps = true;
-
   std::vector<std::unique_ptr<ConcurrentAllocationThread>> threads;
 
   const int kThreads = 4;
@@ -150,6 +149,7 @@ class ConcurrentBlackAllocationThread final : public v8::base::Thread {
 
 UNINITIALIZED_TEST(ConcurrentBlackAllocation) {
   FLAG_concurrent_allocation = true;
+  FLAG_local_heaps = true;
 
   v8::Isolate::CreateParams create_params;
   create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
@@ -157,8 +157,6 @@ UNINITIALIZED_TEST(ConcurrentBlackAllocation) {
   Isolate* i_isolate = reinterpret_cast<Isolate*>(isolate);
   Heap* heap = i_isolate->heap();
 
-  FLAG_local_heaps = true;
-
   std::vector<Address> objects;
 
   base::Semaphore sema_white(0);