sync: Re-enable some migration integration tests

sync: Re-enable some migration integration tests

Removes the "ShouldRunMigrationTest()" check from the migration tests.
This check was preventing the tests from being run, but did not cause
them to emit any errors.

Sets these tests to use the legacy python server, since the in-process
server does not yet support migration.

Removes a DCHECK in StatusChangeChecker, since the MigrationChecker
won't work when that condition is enforced.  We can look into
re-enabling it at some later point.

Disables many of the migration tests.  They've been broken by changes
made to the code since they were disabled.

BUG=392989
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=282654

[rlarocque, 2014-07-11 00:27:00]

Here's the first part of re-enabling these tests.

Some of them are broken and will need to be fixed separately.  I've marked these
as DISABLED to make it more clear that they're not being run.

Please review.

[pval...(no longer on Chromium), 2014-07-11 00:32:51]

lgtm

thanks for catching this and re-enabling

[Nicolas Zea, 2014-07-11 17:48:59]

lgtm

[rlarocque, 2014-07-11 17:54:38]

The CQ bit was checked by rlarocque@chromium.org

[commit-bot: I haz the power, 2014-07-11 17:55:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rlarocque@chromium.org/387763002/1

[commit-bot: I haz the power, 2014-07-11 18:42:49]

Change committed as 282654