Mark URLs with empty schemes as invalid.

components/omnibox/browser/autocomplete_input.cc

Index: components/omnibox/browser/autocomplete_input.cc
diff --git a/components/omnibox/browser/autocomplete_input.cc b/components/omnibox/browser/autocomplete_input.cc
index 7207fc8b5e68ba44e4e354bbc79b4f3317e4d5d1..b3b761b5cb6e37b0aff7ffcb3b6e1c067e5a2b46 100644
--- a/components/omnibox/browser/autocomplete_input.cc
+++ b/components/omnibox/browser/autocomplete_input.cc
@@ -155,6 +155,12 @@ metrics::OmniboxInputType::Type AutocompleteInput::Parse(
   if (first_non_white == base::string16::npos)
     return metrics::OmniboxInputType::INVALID;  // All whitespace.
 
+  // Treat input that beings with a colon as a query. Otherwise the URL

[Peter Kasting, 2016/09/29 04:54:12]

Nit: begins

+  // formatter will attempt to fix it by prepending a scheme, which the user
+  // probably did not want if they explicitly typed a colon at the beginning.
+  if (text[first_non_white] == ':')
+    return metrics::OmniboxInputType::QUERY;

[Peter Kasting, 2016/09/29 04:54:12]

It would be nice to avoid doing this check here, and maybe instead detect this
lower down, ideally without actually looking for an explicit colon.

Where does control flow go if we don't do this here?  You implied ":w" will
become a navigation, but I don't know what exit point below we actually take in
that case.  (Especially depending on whether you make other changes to stuff I
comment on elsewhere.)

+
   // Ask our parsing back-end to help us understand what the user typed.  We
   // use the URLFixerUpper here because we want to be smart about what we
   // consider a scheme.  For example, we shouldn't consider www.google.com:80
@@ -254,13 +260,6 @@ metrics::OmniboxInputType::Type AutocompleteInput::Parse(
   // between an HTTP URL and a query, or the scheme is HTTP or HTTPS, in which
   // case we should reject invalid formulations.
 
-  // If we have an empty host it can't be a valid HTTP[S] URL.  (This should
-  // only trigger for input that begins with a colon, which GURL will parse as a
-  // valid, non-standard URL; for standard URLs, an empty host would have
-  // resulted in an invalid |canonicalized_url| above.)
-  if (!canonicalized_url->has_host())
-    return metrics::OmniboxInputType::QUERY;
-
   // Determine the host family.  We get this information by (re-)canonicalizing
   // the already-canonicalized host rather than using the user's original input,
   // in case fixup affected the result here (e.g. an input that looks like an