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Reason for revert:
The indexeddb_perf tests on all Windows testers regressed in performance significantly. Don't yet know the exact cause, but because the performance drop is significant will revert this change first, and then proceed with the investigation.

Original issue's description:
> Created new Win32 LevelDB environment.
>     
> This change splits ChromiumEnv into two classes: ChromiumEnv/ChromiumEnvPosix.
> ChromiumEnvWin32 was also added which uses the Win32 API - except for logging.
> 
> The default is to create POSIX environments for all platforms for non-IDB
> LevelDB users. For IDB we create a Windows environment on Windows, else a
> POSIX environment like before.
> 
> BUG=222623
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=245135

TBR=dgrogan@chromium.org,alecflett@chromium.org,jsbell@chromium.org,iannucci@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=222623

Review URL: https://codereview.chromium.org/140923005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245270 0039d316-1c4b-4281-b951-d872f2087c98