Revert of [sql] Use memory-mapped I/O for sql::Connection.

Revert of [sql] Use memory-mapped I/O for sql::Connection. (patchset #8 id:140001 of https://codereview.chromium.org/1349863003/ )

Reason for revert:
mmap_enabled_ isn't initialized, causing MSAN failures:

https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Linux_MSAN/5882/layout-test-results/virtual/sharedarraybuffer/fast/workers/constructor-proto-crash-log.txt

STDERR: ==3138==WARNING: MemorySanitizer: use-of-uninitialized-value
STDERR:     #0 0x7fc8068d3a65 in ReleaseCacheMemoryIfNeeded sql/connection.cc:513:7
STDERR:     #1 0x7fc8068d3a65 in sql::Connection::ExecuteAndReturnErrorCode(char const*) sql/connection.cc:943:0
STDERR:     #2 0x7fc8068ca454 in sql::Connection::OpenInternal(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, sql::Connection::Retry) sql/connection.cc:1275:9
STDERR:     #3 0x7fc8068c845f in sql::Connection::Open(base::FilePath const&) sql/connection.cc:367:10
STDERR:     #4 0x7fc806b1b868 in storage::QuotaDatabase::LazyOpen(bool) storage/browser/quota/quota_database.cc:488:14

Original issue's description:
> [sql] Use memory-mapped I/O for sql::Connection.
>
> sql::Connection::Open*() uses PRAGMA mmap_size to enable SQLite's
> memory-mapped I/O.  Additionally instrument to flush dirty pages from
> the page cache after writes.
>
> BUG=489784, 533682
>
> Committed: https://crrev.com/9a1948a4d6d445d5c8e209bdcd1cd050af72060b
> Cr-Commit-Position: refs/heads/master@{#350362}

R=shess@chromium.org
TBR=pavely@chromium.org, pvalenzuela@chromium.org, rmcilroy@chromium.org, shess@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=489784, 533682
Committed: https://chromium.googlesource.com/chromium/src/+/55c3216b15cec4ae024d16960f01ca7d3874dd55

[jbroman, 2015-09-23 22:37:40]

Created Revert of [sql] Use memory-mapped I/O for sql::Connection.

[Scott Hess - ex-Googler, 2015-09-23 22:40:25]

lgtm

[jbroman, 2015-09-23 22:43:59]

The CQ bit was unchecked by jbroman@chromium.org

[jbroman, 2015-09-23 22:44:03]

The CQ bit was checked by jbroman@chromium.org

[Scott Hess - ex-Googler, 2015-09-23 23:26:58]

On 2015/09/23 22:40:25, Scott Hess wrote:
> lgtm

Misuru was asking about this - is the c-q stuck?  Should it be more aggressively
landed?

[jbroman, 2015-09-23 23:27:43]

On 2015/09/23 at 22:40:25, shess wrote:
> lgtm

Not sure why the CQ has ignored this. Landing with "git cl land".

[commit-bot: I haz the power, 2015-09-23 23:29:08]

Patchset 1 (id:??) landed as
https://crrev.com/55c3216b15cec4ae024d16960f01ca7d3874dd55
Cr-Commit-Position: refs/heads/master@{#350386}

[jbroman, 2015-09-23 23:29:29]

Committed patchset #1 (id:1) manually as
55c3216b15cec4ae024d16960f01ca7d3874dd55 (presubmit successful).