[sync] Enable sync credential caching by default for post-M22 builds

[sync] Enable sync credential caching by default for post-M22 builds

Sync credential caching is a Win 8 feature that allows Metro and Desktop
to share sync credentials under some circumstances. The feature is
slated to ship with M23, and was disabled for the M22 branch point.
Now that M22 has been branched off, it is time to re-enable the feature.

This patch turns on the feature by default, and provides users with the
"--disable-sync-credential-caching" flag if the feature must be disabled.

BUG=139712
TEST=Sign in on Win 8 and make sure that "Sync Credentials" is written to the default profile directory

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=151169

[Raghu Simha, 2012-08-09 00:05:00]

Drew, please review. Thanks!

[Raghu Simha, 2012-08-10 17:58:20]

Ping :)

[Andrew T Wilson (Slow), 2012-08-10 21:02:44]

LGTM, but I think you'll need someone in chrome/OWNERS too for your changes to
common/

[Raghu Simha, 2012-08-10 22:42:46]

+Nico for changes to chrome/common.

[Nico, 2012-08-10 23:16:00]

lgtm