Fix protobuf's Python runtime and imports.

Fix protobuf's Python runtime and imports.

Protobuf-generated stubs could fallback to system-wide protobuf.
Also descriptor_pb2.py was generated manually.
Now it's fixed.

BUG=732823

[kraynov, 2017-06-13 15:22:09]

The CQ bit was checked by kraynov@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-06-13 15:22:31]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[kraynov, 2017-06-13 15:22:54]

Description was changed from

==========
Fix protobuf's Python runtime and imports.

Protobuf-generated stubs could fallback to system-wide protobuf.
Also descriptor_pb2.py now generated automatically.

BUG=732823
==========

to

==========
Fix protobuf's Python runtime and imports.

Protobuf-generated stubs could fallback to system-wide protobuf.
Also descriptor_pb2.py was generated manually.
Now it's fixed.

BUG=732823
==========

[commit-bot: I haz the power, 2017-06-13 15:34:14]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-06-13 15:34:15]

Dry run: Try jobs failed on following builders:
  ios-device on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/builds...)

[wychen, 2017-06-14 03:35:00]

wychen@chromium.org changed reviewers:
+ wychen@chromium.org

[wychen, 2017-06-14 03:35:00]

I like this approach.

[kraynov, 2017-06-15 09:46:55]

The CQ bit was checked by kraynov@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-06-15 09:47:04]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-06-15 09:55:53]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-06-15 09:55:54]

Dry run: Try jobs failed on following builders:
  mac_chromium_compile_dbg_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)