Note to self, or to whomever works on this: should probably also fix LevelDBWrapperImpl::CommitChanges to bail out if (!commit_batch_) rather than the current if (commit_batch_). (I don't think the current code would ever end up committing anything).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2d68b588bdb1940e05b5e1fe7027974f1d574e71

commit 2d68b588bdb1940e05b5e1fe7027974f1d574e71
Author: mek <mek@chromium.org>
Date: Thu Dec 22 19:09:28 2016

Don't duplicate values in LevelDBWrapperImpl::CommitBatch.

Instead just store keys and lookup values when actually committing to
the database.

BUG= 644376 

Review-Url: https://codereview.chromium.org/2595183002
Cr-Commit-Position: refs/heads/master@{#440463}

[modify] https://crrev.com/2d68b588bdb1940e05b5e1fe7027974f1d574e71/content/browser/leveldb_wrapper_impl.cc
[modify] https://crrev.com/2d68b588bdb1940e05b5e1fe7027974f1d574e71/content/browser/leveldb_wrapper_impl.h