Don't try to create a verbatim match with an empty input.
## Description of the problem
On iOS, tapping on an empty omnibox triggers a request to the
ClipboardUrlProvider.
The ClipboardURLProvider then calls VerbatimMatchForURL with an empty |input| (if the omnibox was empty), which eventually triggers a
DCHECK_GT in |AutocompleteMatch::ClassifyLocationInString|:
// Classifying an empty match makes no sense and will lead to validation
// errors later.
DCHECK_GT(match_length, 0U);
## Description of the solution
This CL makes it forbidden to pass an empty input to
|VerbatimMatchForURL|, and fixes the clipboard_url_provider.
BUG=625313
Review-Url: https://codereview.chromium.org/2124563002
Cr-Commit-Position: refs/heads/master@{#405136}
3 files changed
