GDataDB support with leveldb.

GDataDB support with leveldb.

* Define GDataDB interface with methods to Put, Get and Delete. Also define a path-based iterator.
* GDataLevelDB implements GDataDB using leveldb. 
* Add methods SerializeToString and FromProtoString to serialize GDataEntry to strings and vice versa.
* GDataDBTests test Put, Get, Delete for files and directories.
* Iterator tests in GDataDBTests.
* GDataDBFactory class to create GDataLevelDB instance.
* Update deps to allow leveldatabase.

TODO:
* There is no integration with GDataRootDirectory/GDataFileSystem yet.

BUG=chromium-os:29232
TEST=unittests pass.
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=133833

[achuithb, 2012-04-25 00:33:57]

Previous CL here:
http://codereview.chromium.org/10168025/

Reverted due to deps failure here:
http://build.chromium.org/p/chromium/builders/Linux%20Builder%20x64/builds/42...

[achuithb, 2012-04-25 01:13:06]

Identical to http://codereview.chromium.org/10168025/ except for addition of
DEPS.

[achuithb, 2012-04-25 01:18:50]

Zel requests shorter prefix.

[zel, 2012-04-25 01:21:34]

lgtm

[achuithb, 2012-04-25 01:22:06]

On 2012/04/25 01:21:34, zel wrote:
> lgtm

Thanks Zel!

[xiyuan, 2012-04-25 01:40:25]

check_deps fail seems to be real and you might want to fix that.

ERROR in
/mnt/data/b/build/slave/linux/build/src/chrome/browser/chromeos/gdata/gdata_leveldb.cc
Illegal include: "leveldb/write_batch.h"
    Because of no rule applying

[achuithb, 2012-04-25 01:50:02]

On 2012/04/25 01:40:25, xiyuan wrote:
> check_deps fail seems to be real and you might want to fix that.
> 
> ERROR in
>
/mnt/data/b/build/slave/linux/build/src/chrome/browser/chromeos/gdata/gdata_leveldb.cc
> Illegal include: "leveldb/write_batch.h"
>     Because of no rule applying

I believe this CL fixes the DEPS failure? There was an earlier CL that didn't
have this fix. Are you at TOT?

[xiyuan, 2012-04-25 01:56:07]

On 2012/04/25 01:50:02, achuith.bhandarkar wrote:
> On 2012/04/25 01:40:25, xiyuan wrote:
> > check_deps fail seems to be real and you might want to fix that.
> > 
> > ERROR in
> >
>
/mnt/data/b/build/slave/linux/build/src/chrome/browser/chromeos/gdata/gdata_leveldb.cc
> > Illegal include: "leveldb/write_batch.h"
> >     Because of no rule applying
> 
> I believe this CL fixes the DEPS failure? There was an earlier CL that didn't
> have this fix. Are you at TOT?

You are right. I was on r133818.