[heap] Fix allocation observer for young large objects

The allocation observer step should be called only after the page flags
of the young large object are properly set up.

Bug: chromium:852420
Change-Id: I9f537a7c1d6b7aa15ccbe58006e3957a2ec2ab5c
Reviewed-on: https://chromium-review.googlesource.com/c/1477735Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59696}

src/heap/spaces.cc

@@ -3463,6 +3463,7 @@ AllocationResult LargeObjectSpace::AllocateRaw(int object_size,
       heap()->incremental_marking()->marking_state()->IsBlack(object));
   page->InitializationMemoryFence();
   heap()->NotifyOldGenerationExpansion();
+  AllocationStep(object_size, object->address(), object_size);
   return object;
 }
 
@@ -3479,7 +3480,6 @@ LargePage* LargeObjectSpace::AllocateLargePage(int object_size,
 
   heap()->CreateFillerObjectAt(object->address(), object_size,
                                ClearRecordedSlots::kNo);
-  AllocationStep(object_size, object->address(), object_size);
   return page;
 }
 
@@ -3779,6 +3779,7 @@ AllocationResult NewLargeObjectSpace::AllocateRaw(int object_size) {
   page->InitializationMemoryFence();
   DCHECK(page->IsLargePage());
   DCHECK_EQ(page->owner()->identity(), NEW_LO_SPACE);
+  AllocationStep(object_size, result->address(), object_size);
   return result;
 }