Omnibox: Make HQP Show Scheme At Right Times

In particular, the HistoryQuick provider should show the scheme of a URL
match it's suggesting if there is a match in the scheme.

The previous code was entirely wrong and only worked for prefix matches.

TBR=sky,pkasting
BUG=324746

Review URL: https://codereview.chromium.org/113773003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241052 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241052
Put ignore autocomplete='off' behind a flag. Restores the basic
autocomplete='off' semantics, but creates a flag to ignore autocomplete='off' so
we can choose which way to go for release.

BUG=177288

Review URL: https://codereview.chromium.org/109343002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241053 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241053