Retrieve client_id from GoogleUpdateSettings when its missing from Local State.

Precursor refactoring CL @ https://codereview.chromium.org/365133005/

Precursor kInstallDate move to metrics_pref_names @ https://codereview.chromium.org/370813003/

This is the Windows implementation, POSIX implementation to follow in https://codereview.chromium.org/377713002/ (easier to develop and test on Linux in a follow-up CL)

BUG=391338

Review URL: https://codereview.chromium.org/372473004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284805 0039d316-1c4b-4281-b951-d872f2087c98
22 files changed