[turbofan] split compilation stats off from HStatistics and track high water marks

src/compiler/zone-pool.cc

Index: src/compiler/zone-pool.cc
diff --git a/src/compiler/zone-pool.cc b/src/compiler/zone-pool.cc
index 8276023522962e01762e0dd6e85b8ac0469391ab..179988d418f15a469b775a26a2d72065f2a4ad72 100644
--- a/src/compiler/zone-pool.cc
+++ b/src/compiler/zone-pool.cc
@@ -9,7 +9,9 @@ namespace internal {
 namespace compiler {
 
 ZonePool::StatsScope::StatsScope(ZonePool* zone_pool)
-    : zone_pool_(zone_pool), max_allocated_bytes_(0) {
+    : zone_pool_(zone_pool),
+      total_allocated_bytes_at_start_(zone_pool->GetTotalAllocatedBytes()),
+      max_allocated_bytes_(0) {
   zone_pool_->stats_.push_back(this);
   for (auto zone : zone_pool_->used_) {
     size_t size = static_cast<size_t>(zone->allocation_size());
@@ -46,6 +48,11 @@ size_t ZonePool::StatsScope::GetCurrentAllocatedBytes() {
 }
 
 
+size_t ZonePool::StatsScope::GetTotalAllocatedBytes() {
+  return zone_pool_->GetTotalAllocatedBytes() - total_allocated_bytes_at_start_;
+}
+
+
 void ZonePool::StatsScope::ZoneReturned(Zone* zone) {
   size_t current_total = GetCurrentAllocatedBytes();
   // Update max.