[zone] Fix zone segment pooling size limits

BUG=chromium:655129

Review-Url: https://codereview.chromium.org/2520903002
Cr-Commit-Position: refs/heads/master@{#41138}

src/zone/accounting-allocator.cc

@@ -59,7 +59,8 @@ void AccountingAllocator::ConfigureSegmentPool(const size_t max_pool_size) {
   size_t total_size = fits_fully * full_size;
 
   for (size_t power = 0; power < kNumberBuckets; ++power) {
-    if (total_size + (size_t(1) << power) <= max_pool_size) {
+    if (total_size + (size_t(1) << (power + kMinSegmentSizePower)) <=
+        max_pool_size) {
       unused_segments_max_sizes_[power] = fits_fully + 1;
       total_size += size_t(1) << power;
     } else {