[sql] Increase database chunk size for large databases.
[sql] Increase database chunk size for large databases.

SQLite implements a hint to request the databases be truncated or
expanded to multiples of a chunk size.  This was originally implemented
to reduce filesystem fragmentation, and it also can improve performance
because file sizes don't vary as much.

For a memory-mapped database, it also reduces the number of calls to
adjust the memory map when the database size changes.

BUG=551108

Review URL: https://codereview.chromium.org/1402373007

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#358121}

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