Increase old generation size from 2 GB to 4 GB for the 16 GB physical memory configuration

The current V8HugeMaxOldGenerationSize feature increases the JS heap size for
systems with larger than 16 GB physical memory. This cl adds support for 16 GB
configuration.

Because a small portion of memory is reserved by hardware, the physical memory
calculation here is rounded up to GB so the actual installed memory is checked.

Bug:chromium:958974

Change-Id: Idaf2e03a43ba6c3c40bb771296d06b87032c2725
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1734038
Commit-Queue: Maggie Chen <magchen@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63104}

src/heap/heap.cc

@@ -270,10 +270,11 @@ size_t Heap::MinOldGenerationSize() {
 size_t Heap::MaxOldGenerationSize(uint64_t physical_memory) {
   size_t max_size = V8HeapTrait::kMaxSize;
   // Finch experiment: Increase the heap size from 2GB to 4GB for 64-bit
-  // systems with physical memory bigger than 16GB.
+  // systems with physical memory bigger than 16GB. The physical memory
+  // is rounded up to GB.
   constexpr bool x64_bit = Heap::kPointerMultiplier >= 2;
   if (FLAG_huge_max_old_generation_size && x64_bit &&
-      physical_memory / GB > 16) {
+      (physical_memory + 512 * MB) / GB >= 16) {
     DCHECK_EQ(max_size / GB, 2);
     max_size *= 2;
   }