Version: ToT (96452d073371da1e1ab7eb1ef724df0926f76547-refs/heads/master@{#386464})
OS: All

What steps will reproduce the problem?
(1) Create a custom search engine with a keyword (e.g. "cr"), whose URL is something like "http://www.google.com/search?q=%s@chromium.org".
(2) Repeatedly enter "cr jbroman" into the omnibox, hitting enter each time.
(3) Eventually, it will offer to autocomplete (HistoryQuickProvider). However, the autocomplete suggestion will be "jbroman@chromium.org", choosing which leads to a search for "jbroman@chromium.org@chromium.org".

Debugging this, it looks like TemplateURLRef assumes that the replacements it provides will always fill a full URL component (e.g. query param). While going from query to URL works fine (it will substitute in the query parameter, leaving the suffix intact), when going in the opposite direction (TemplateURLRef::ExtractSearchTermsFromURL) it just locates the corresponding query key ("q"), and takes the whole value ("jbroman@chromium.org") as the extracted value.

Ideally, it would extract "jbroman" (being aware of the prefix/suffix). Another, less convenient, alternative might be not to offer autocomplete suggestions for search engines of this type.

I'd fix this myself, but it seems to have larger implications for components/search_engines/.