Make chrome_elf use thunks instead of function pointers.

1. Add functionality to ServiceResolverThunk to copy a thunk without patching.
2. Move chrome_elf thunk-handling code to a common location.
3. Use a thunk instead of a f'n ptr for redirects.

BUG=334379

Review URL: https://codereview.chromium.org/183833004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255151 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255151