Tame the proliferation of UserContext constructors

Tame the proliferation of UserContext constructors

UserContext offered a number of constructors aimed at specific use cases.
One of these ended up being used as a poor man's copy constructor that
took separate arguments to populate the various UserContext members. It
had already gotten out of sync with the full UserContext state (there are
8 members but this constructor copied only 6). The problem would likely
have become only worse in the future.

This CL replaces the existing constructors with a more well-defined set:
* A default constructor
* An actual copy constructor that copies all members
* A constructor that takes a |user_id|, which is required in almost all
  cases
The copy constructor also replaces the ad-hoc CopyFrom() method.

AuthAttemptState also offered several constructors, two of which took
credentials in the form of a |user_context| while one took |username|
and |password| separately. The CL combines these into a single
constructor that always takes credentials as a |user_context|.

BUG=367847
TEST=Updated unit and browser tests

TBR=pamg (chrome/browser/managed_mode/chromeos/manager_password_service.cc)

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271258

[bartfab (slow), 2014-05-15 12:44:19]

Hi Denis,

Could you take a look please?

[Denis Kuznetsov (DE-MUC), 2014-05-15 14:23:57]

lgtm

[bartfab (slow), 2014-05-16 08:05:49]

The CQ bit was checked by bartfab@chromium.org

[commit-bot: I haz the power, 2014-05-16 08:05:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/bartfab@chromium.org/290483003/20001

[Nikita (slow), 2014-05-16 08:08:19]

lgtm

[commit-bot: I haz the power, 2014-05-16 09:58:07]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg/builds/18...)
  linux_chromium_chromeos_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_chrome...)

[commit-bot: I haz the power, 2014-05-16 11:03:36]

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

[commit-bot: I haz the power, 2014-05-16 11:03:36]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_chrome...)

[bartfab (slow), 2014-05-17 07:44:19]

The CQ bit was checked by bartfab@chromium.org

[commit-bot: I haz the power, 2014-05-17 07:44:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/bartfab@chromium.org/290483003/40001

[commit-bot: I haz the power, 2014-05-17 19:23:48]

Change committed as 271258