Use shared shared URLRequestContextGetter for all gcd_private sessions

Use shared shared URLRequestContextGetter for all gcd_private sessions

PrivetV3ContextGetter is context getter for gcd_private sessions.
It's owned by singleton of GcdPrivateAPIImpl.

BUG=524788
Committed: https://crrev.com/60701c6012a69ffab8b2fe8b9f19e98469c1fc40
Cr-Commit-Position: refs/heads/master@{#359782}

[Vitaly Buka (NO REVIEWS), 2015-11-14 01:56:04]

vitalybuka@chromium.org changed reviewers:
+ alekseys@chromium.org

[Vitaly Buka (NO REVIEWS), 2015-11-14 01:56:12]

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

[commit-bot: I haz the power, 2015-11-14 01:56:38]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1441403005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1441403005/1

[commit-bot: I haz the power, 2015-11-14 02:20:02]

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

[commit-bot: I haz the power, 2015-11-14 02:20:03]

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

[Aleksey Shlyapnikov, 2015-11-14 02:22:37]

lgtm

[Vitaly Buka (NO REVIEWS), 2015-11-15 03:09:53]

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

[commit-bot: I haz the power, 2015-11-15 03:10:31]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1441403005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1441403005/1

[commit-bot: I haz the power, 2015-11-15 03:31:34]

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

[commit-bot: I haz the power, 2015-11-15 03:31:35]

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

[Vitaly Buka (NO REVIEWS), 2015-11-15 06:27:05]

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

[commit-bot: I haz the power, 2015-11-15 06:27:09]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1441403005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1441403005/20001

[commit-bot: I haz the power, 2015-11-15 12:10:56]

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

[commit-bot: I haz the power, 2015-11-15 12:11:02]

Dry run: This issue passed the CQ dry run.

[Vitaly Buka (NO REVIEWS), 2015-11-15 19:45:10]

The CQ bit was checked by vitalybuka@chromium.org

[Vitaly Buka (NO REVIEWS), 2015-11-15 19:45:11]

The patchset sent to the CQ was uploaded after l-g-t-m from
alekseys@chromium.org
Link to the patchset: https://codereview.chromium.org/1441403005/#ps20001
(title: " ")

[commit-bot: I haz the power, 2015-11-15 19:45:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1441403005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1441403005/20001

[commit-bot: I haz the power, 2015-11-15 19:48:59]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-15 19:49:48]

Patchset 2 (id:??) landed as
https://crrev.com/60701c6012a69ffab8b2fe8b9f19e98469c1fc40
Cr-Commit-Position: refs/heads/master@{#359782}