[Android] Only allow one account per tab for autologin infobars

We should always have one and only one account per tab at most and allowing more than one is causing bugs when don't clear them properly (as a result of an infobar being dismissed by the native side).


BUG=295871

Review URL: https://codereview.chromium.org/25730003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226658 0039d316-1c4b-4281-b951-d872f2087c98
[Clean up] Remove unused method SetSuggestionToPrefetch from BrowserInstantController.

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/25793003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226659 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226658
SVN changes up to revision 226659