Revamp the MigrateBrowserPrefs and MigrateUserPrefs code.

chrome/browser/profiles/profile_impl.cc

Index: chrome/browser/profiles/profile_impl.cc
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 4fcb7e476868d7a0b1bcfdf970ca424aa082f8fc..def96c521a37ece6b7cd2f99c922286cccf1dd5e 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -855,10 +855,9 @@ void ProfileImpl::OnPrefsLoaded(bool success) {
     return;
   }
 
-  // TODO(mirandac): remove migration code after 6 months (crbug.com/69995).
+  // Migrate all obsolete prefs.

[gab, 2015/02/20 20:33:57]

rm "all" (it's implicit IMO)

PS: I like "obsolete" perhaps add that to the migration method's names? e.g.
MigrateObsoleteBrowserPrefs() and MigrateObsoleteProfilePrefs() -- oh yea, also,
I prefer ProfilePrefs to UserPrefs as it's more explicit (i.e. a user can have
multiple profiles).

[rkaplow, 2015/02/20 21:58:08]

Seems fine. Note that some of the work is done by names that mirror the current
name, eg. autofill::AutofillManager::MigrateUserPrefs

In the long run those will go away so it seems fine for a temporary discrepancy.

   if (g_browser_process->local_state())
     chrome::MigrateBrowserPrefs(this, g_browser_process->local_state());
-  // TODO(ivankr): remove cleanup code eventually (crbug.com/165672).
   chrome::MigrateUserPrefs(this);
 
   // |kSessionExitType| was added after |kSessionExitedCleanly|. If the pref