Mark URLs with empty schemes as invalid.

components/url_formatter/url_fixer.cc

Index: components/url_formatter/url_fixer.cc
diff --git a/components/url_formatter/url_fixer.cc b/components/url_formatter/url_fixer.cc
index 53abe4e0c4a910aa2a065160af3f35c0533352be..cf60f43d3b57874a0ebe1c5ccda1e2817ea3e961 100644
--- a/components/url_formatter/url_fixer.cc
+++ b/components/url_formatter/url_fixer.cc
@@ -480,7 +480,8 @@ std::string SegmentURLInternal(std::string* text, url::Parsed* parts) {
 
   // Construct the text to parse by inserting the scheme.
   std::string inserted_text(scheme);
-  inserted_text.append(url::kStandardSchemeSeparator);
+  if (first_nonwhite == text->end() || *first_nonwhite != ':')
+    inserted_text.append(url::kStandardSchemeSeparator);  // Add "://".

[Peter Kasting, 2016/10/05 00:56:30]

Nit: After your explanation, I understand why this works.  GURL fixing up
"foo:bar" into "foo://bar" was the missing piece.

This seems a little unclear, so it'd be nice to do one of the following:

(1) Skip over the colon in the input:

  inserted_text.append(url::kStandardSchemeSeparator);
  // Assume a leading colon was meant to be a scheme separator (which we can
  // thus skip, since we just added this).
  if (first_nonwhite != text->end() && *first_nonwhite == ':')
    ++first_nonwhite;

(2) Add a comment about GURL's behavior here:

  // Assume a leading colon was meant to be a scheme separator (which GURL will
  // fix up for us into the full "://").  Otherwise add the separator ourselves.
  if (first_nonwhite == text->end() || *first_nonwhite != ':')
    inserted_text.append(url::kStandardSchemeSeparator);

[brettw, 2016/10/05 05:10:12]

I did the second.

   std::string text_to_parse(text->begin(), first_nonwhite);
   text_to_parse.append(inserted_text);
   text_to_parse.append(first_nonwhite, text->end());