mojo: Add deserialization to python structs.

mojo: Add deserialization to python structs.

This is a reland of https://codereview.chromium.org/588493002 using buffer on
bytearray before trying to call unpack_from because python 2.7.3 and earlier
doesn't handle unpacking a bytearray directly.

BUG=415491
R=sdefresne@chromium.org,cmasone@chromium.org

Committed: https://crrev.com/25606073cbdfc4772a0caaa23a624a83293fbadc
Cr-Commit-Position: refs/heads/master@{#295716}

[qsr, 2014-09-19 14:02:55]

Ok, 3rd time is the charm.

This time I downloaded and install python 2.7.5, 2.7.4 and 2.7.3 until I could
reproduce and fix it. It should work, unless the bot is in an even earlier
version of python. Unfortunately, the build log doesn't contain the information.

[sdefresne, 2014-09-19 15:18:31]

https://codereview.chromium.org/584893002/diff/20001/mojo/public/python/mojo/...
File mojo/public/python/mojo/bindings/serialization.py (right):

https://codereview.chromium.org/584893002/diff/20001/mojo/public/python/mojo/...
mojo/public/python/mojo/bindings/serialization.py:82: if not isinstance(data,
buffer):
Why not simply "data = buffer(data)"? I've tested, it works, it create a new
buffer instance but backed with the same store. I'm good with the actual code,
mostly interested to know if you tested the other version and found it did not
work or just did not think or doing it.

[sdefresne, 2014-09-19 15:18:37]

lgtm

[qsr, 2014-09-19 15:45:27]

https://codereview.chromium.org/584893002/diff/20001/mojo/public/python/mojo/...
File mojo/public/python/mojo/bindings/serialization.py (right):

https://codereview.chromium.org/584893002/diff/20001/mojo/public/python/mojo/...
mojo/public/python/mojo/bindings/serialization.py:82: if not isinstance(data,
buffer):
On 2014/09/19 15:18:30, sdefresne wrote:
> Why not simply "data = buffer(data)"? I've tested, it works, it create a new
> buffer instance but backed with the same store. I'm good with the actual code,
> mostly interested to know if you tested the other version and found it did not
> work or just did not think or doing it.

 Just to prevent creating some more object for no gain. This method will be
recursively called when deserialize a member that is itself a struct, and in
that case, it will be given a buffer. So, checking this prevent another object
to be created.

[qsr, 2014-09-19 15:45:40]

The CQ bit was checked by qsr@chromium.org

[commit-bot: I haz the power, 2014-09-19 15:46:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/584893002/20001

[commit-bot: I haz the power, 2014-09-19 16:12:46]

Committed patchset #2 (id:20001) as 695b1655fdfff3e060aaedffee15ff69428b7d1c

[commit-bot: I haz the power, 2014-09-19 16:13:19]

Patchset 2 (id:??) landed as
https://crrev.com/25606073cbdfc4772a0caaa23a624a83293fbadc
Cr-Commit-Position: refs/heads/master@{#295716}