[heap] Clear from space after garbage collection.

Bug: chromium:829771
Change-Id: I9e71e6cbba347dd6951e5415332e5178df9b5122
Reviewed-on: https://chromium-review.googlesource.com/1041685
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52957}

src/heap/heap.cc

@@ -920,10 +920,7 @@ void Heap::DeoptMarkedAllocationSites() {
 
 void Heap::GarbageCollectionEpilogue() {
   TRACE_GC(tracer(), GCTracer::Scope::HEAP_EPILOGUE);
-  // In release mode, we only zap the from space under heap verification.
-  if (Heap::ShouldZapGarbage()) {
-    ZapFromSpace();
-  }
+  ZapFromSpace();
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
@@ -3844,12 +3841,13 @@ void Heap::VerifyCountersBeforeConcurrentSweeping() {
 
 void Heap::ZapFromSpace() {
   if (!new_space_->IsFromSpaceCommitted()) return;
+
   for (Page* page :
        PageRange(new_space_->FromSpaceStart(), new_space_->FromSpaceEnd())) {
-    for (Address cursor = page->area_start(), limit = page->area_end();
-         cursor < limit; cursor += kPointerSize) {
-      Memory::Address_at(cursor) = static_cast<Address>(kFromSpaceZapValue);
-    }
+    memory_allocator()->ZapBlock(page->area_start(), page->area_size(),
+                                 Heap::ShouldZapGarbage()
+                                     ? kFromSpaceZapValue
+                                     : kClearedFreeMemoryValue);
   }
 }