[snapshot] Reduce serialization chunk size to 4K.

This change may slow down deserialization of the snapshot but may result in less fragmentation.

Bug: v8:7887
Change-Id: Id8bb9f1a561b08b7ae0f10b80aa77bc00eb23172
Reviewed-on: https://chromium-review.googlesource.com/1125722Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54198}

src/flag-definitions.h

@@ -1080,7 +1080,8 @@ DEFINE_BOOL(profile_deserialization, false,
             "Print the time it takes to deserialize the snapshot.")
 DEFINE_BOOL(serialization_statistics, false,
             "Collect statistics on serialized objects.")
-DEFINE_UINT(serialization_chunk_size, 0, "Custom size for serialization chunks")
+DEFINE_UINT(serialization_chunk_size, 4096,
+            "Custom size for serialization chunks")
 
 // Regexp
 DEFINE_BOOL(regexp_optimization, true, "generate optimized regexp code")