Fix handling of same-skeleton domains in IDN spoof checker

A previous fix for bug 898343 attempted to handle skeletons that are the same as their domains (e.g. test[.]net).

The fix introduced an early return which caused skeleton lookups to incorrectly match subtrings:
If a domain name contained a top domain as its prefix, spoof checker assumed a skeleton match without checking if it reached the end of the search string (i.e. the skeleton being looked up).
E.g. Skeleton of atést[.]net (atest[.]net) matched the skeleton of test[.]net (test[.]net).

This CL properly checks that all of the search string is consumed before returning a match.

Bug: 925199
Change-Id: Ia548ea686915463e0f93e6bce1bad5721f324821
Reviewed-on: https://chromium-review.googlesource.com/c/1437716
Commit-Queue: Mustafa Emre Acer <meacer@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626867}

components/url_formatter/idn_spoof_checker.cc

@@ -35,17 +35,14 @@ class TopDomainPreloadDecoder : public net::extras::PreloadDecoder {
     if (!reader->Next(&is_same_skeleton))
       return false;
 
+    std::string top_domain;
     if (is_same_skeleton) {
-      *out_found = true;
-      result_ = search;
-      return true;
-    }
-
+      top_domain = search;
+    } else {
       bool has_com_suffix = false;
       if (!reader->Next(&has_com_suffix))
         return false;
 
-    std::string top_domain;
       for (char c;; top_domain += c) {
         huffman_decoder().Decode(reader, &c);
         if (c == net::extras::PreloadDecoder::kEndOfTable)
@@ -53,6 +50,7 @@ class TopDomainPreloadDecoder : public net::extras::PreloadDecoder {
       }
       if (has_com_suffix)
         top_domain += ".com";
+    }
 
     if (current_search_offset == 0) {
       *out_found = true;

components/url_formatter/url_formatter_unittest.cc

@@ -1012,8 +1012,21 @@ const IDNTestCase idn_cases[] = {
 
     // Test that top domains whose skeletons are the same as the domain name are
     // handled properly. In this case, tést.net should match test.net top
-    // domain.
+    // domain and not be converted to unicode.
     {"xn--tst-bma.net", L"t\x00e9st.net", false},
+    // Variations of the above, for testing crbug.com/925199.
+    // some.tést.net should match test.net.
+    {"some.xn--tst-bma.net", L"some.t\x00e9st.net", false},
+    // The following should not match test.net, so should be converted to
+    // unicode.
+    // ést.net (a suffix of tést.net).
+    {"xn--st-9ia.net", L"\x00e9st.net", true},
+    // some.ést.net
+    {"some.xn--st-9ia.net", L"some.\x00e9st.net", true},
+    // atést.net (tést.net is a suffix of atést.net)
+    {"xn--atst-cpa.net", L"at\x00e9st.net", true},
+    // some.atést.net
+    {"some.xn--atst-cpa.net", L"some.at\x00e9st.net", true},
 
     // Modifier-letter-voicing should be blocked (wwwˬtest.com).
     {"xn--wwwtest-2be.com", L"www\x02ectest.com", false},