Removed HandleBufferDataImmediate.

BUG=

Review URL: https://codereview.chromium.org/26369002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228035 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228035
Expose PlatformFileLock/Unlock, fix locking in Chromium's leveldb Env

The base::CreatePlatformFile() flags PLATFORM_FILE_EXCLUSIVE_READ/WRITE
are ineffective on existing files on POSIX, and can't be used to
implement the locking scheme required by leveldb.

Add PlatformFileLock/Unlock which have the correct semantics, and
use those in ChromiumEnv. Also, crib code from leveldb's env_posix.cc
to handle in-process exclusivity which is not guaranteed by
file locks.

BUG=245471

Review URL: https://codereview.chromium.org/26306003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228036 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228036