[Mac] Fix the custom homepages preferences to:
1) Make it actually work again.
2) Change the model so that it doesn't get into an infinite recursion cycle
trying to update the model, notify observers, and then re-update.
BUG=49320
TEST=Chromium-->Preferences. Add custom home pages. Close Preferences and reopen. They are still there.
TEST=Open 3 web pages in tabs. Chromium-->Preferences. Use Current homepages. Close Preferences and reopen. They are still there.
TEST=With custom homepages set, go to Chromium-->Preferences-->UtH-->Reset to Defaults. Go back to Basics. No more custom homepages.
Review URL: http://codereview.chromium.org/3023023
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@53961 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed
