Store profile avatar to preferences

This change adds a preference to store avatar icons.

For this change I extended the idea of kProfileAvatarIconMap pref into a full blown class. The class is responsible for mantaining a list of sorted profiles that can be displayed without having to load profiles from disk.

Once this is chcked in there are several TODOs:
  - remove the ProfileManager::GetNumberOfProfiles(), etc... functions that I added earlier
  - add UI to customize the avatar icon
  - create a single instance of the new ProfileInfoCache object some where. Maybe from ProfileManager?

BUG=
TEST=


Review URL: http://codereview.chromium.org/7155015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@90622 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index 1499e75..5e62e81 100644
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -1751,6 +1751,8 @@
         'browser/profiles/profile_impl.h',
         'browser/profiles/profile_impl_io_data.cc',
         'browser/profiles/profile_impl_io_data.h',
+        'browser/profiles/profile_info_cache.cc',
+        'browser/profiles/profile_info_cache.h',
         'browser/profiles/profile_io_data.cc',
         'browser/profiles/profile_io_data.h',
         'browser/profiles/profile_keyed_service_factory.cc',